The Institute for Fiscal Studies is warning that the chances of Reeves meeting her fiscal rules are "a coin toss"
The think tank says that more tax rises might come in the Autumn Budget, with director Paul Johnson saying: "there's a good chance that economic ... forecasts will deteriorate"
The warning comes as Chancellor Rachel Reeves says the UK is speaking to the US to try and make a deal that would avoid the implementation of 25% tariffs on cars and car parts
Earlier, the government's forecaster halved its growth projection for the year to 2025 and warned Reeves that UK and global economic uncertainty could derail her plans
The chancellor says there will be a £9.9bn surplus in day-to-day spending in five years but the OBR says it is a "very small margin" and risks are heightened by "significant uncertainty" in the UK and global economy
How could the Spring Statement affect you? Our cost of living correspondent breaks down the changes
Rachel Reeves asked if she has concerns about Trump's car tariffs
Image source, ReutersChancellor Rachel Reeves has left Downing Street and is now heading to the Commons.
At 12.30 she will deliver the speech we've been building up to all morning.
There's a lot to happen before then though - not least PMQs - so stay tuned.
Kevin Peachey
Cost of living correspondent
Tighter eligibility criteria for disability payments will have a direct impact on many thousands of benefit claimants.
However, those changes are centred on Personal Independence Payments (Pip) which are paid in England, Wales and Northern Ireland - but not Scotland.
Universal Credit, on the other hand, is UK-wide.
Today there should be more detail on where cuts will come and what sorts of benefits are affected.
In the case of Scotland, there may not be a direct impact initially - but a reduction in Treasury funding allocated to the administration in Scotland for welfare benefits could be felt.
Dearbail Jordan
Business reporter
The Office for Budget Responsibility (OBR) is an independent group of economists and analysts which, basically, marks the government's homework.
It looks at official plans for both tax and spending, and forecasts what effect they will have on the UK economy as well as on the public finances.
The OBR is not part of the government but works closely with the Treasury. It releases two reports a year, coinciding with the Budget as well as events like the Spring Statement.
The idea of the OBR is to show that the government is being responsible with the nation's finances, that it can pay its debts.
Financial markets - which determine some interest rates that the government pays on its borrowing - take a great deal of notice of what the OBR says.
But the thing to remember about the OBR is that it makes predictions. Its forecasts are not facts, rather guidance on what could happen based on what the government tells it.
Emily Atkinson
Live page editor
OBR-Treasury clash: Last night, it emerged the OBR - the independent body which inspects the Treasury's plans - was disputing the government's estimates about how much welfare changes can save.
More cuts: Ministers say they can save £5bn - but the OBR reckons it's more like £3.4bn. Now we're expecting Chancellor Rachel Reeves to announce additional cuts in her Spring Statement.
Inflation: At 07:00 this morning, the latest official inflation statistics were published. At 2.8%, the rate of price rises was slightly lower than expected. Despite that modest good news, Defence Secretary John Healey said the country should expect the chancellor to deliver a "tough, strong statement in tough times".
Final discussions: A short time ago, the cabinet finished meeting for their final pre-statement discussions. Soon, it will be all eyes on the Commons to find out what plans they signed off.
Hayley Clarke & Emma Pengelly
Reporters
Image source, SuppliedElspeth with her assistance dog Podge
Elspeth Edwards, 20, from Worcester, is very worried about the disability cuts.
She currently receives Pip and LCWRA (Limited Capability for Work and Work-Related Activity) - the universal credit health top up, which the government has said it plans to cut for those aged 18-22.
Elspeth says that she is unable to work due to her conditions, as she faints multiple times a day, is in “immense pain constantly” and suffers from severe fatigue.
Taking away the support won’t change her ability to work, but it will “take away my freedom”, she says, adding that she wants to contribute to society.
“These payments have allowed me to have some independence - I’ve been able to afford rent and food for myself and my assistance dog and I’ve finally had the support system to start applying at my local university to study astrophysics.
“Taking away the money will take away my freedom and my chance at a career in astrophysics.”
Faisal Islam
Economics editor
A tough last assessment of Rachel Reeves' plans by government forecaster the Office for Budget Responsibility (OBR) has lowered the £5bn she expected to save from last week’s welfare reform package.
It looks a little messy to have wrangling over these numbers.
The OBR predicts that many claimants facing losses of thousands of pounds of health and disability benefits will instead claim for more severe conditions.
Some of the assessment criteria are subjective, and a little fuzzy.
As has occurred historically, there would be a massive incentive - worth thousands of pounds - for more people to claim that their disability was more severe on the points-based system for Personal Independence Payments.
To make up some of that gap, there will be relatively small extra welfare cuts, mainly affecting future eligibility.
Glenn Campbell
Political editor, BBC Scotland
It’s hard to tell what the Spring Statement will mean for Scotland.
There is a direct link to the money that comes to the Scottish government to fund devolved public services with what is spent on those equivalent services in England.
So, where there is a cut to spending on welfare - a benefit that has already been devolved to Scotland - then that’s likely to mean a squeeze to the money that comes to the Scottish government, to spend in that area or however it chooses.
I’m not sure it will be easy to work out instantly what the squeeze might be, but you can be sure that the Scottish government and its SNP MPs will warn against any return to what they would see as austerity and will oppose some of the cuts that are being proposed by the Labour government.
John Campbell and Clodagh Rice
BBC News NI business unit
Northern Ireland executive ministers will find out later what the chancellor's revised spending plans are likely to mean for Stormont budgets.
Rachel Reeves may announce lower spending increases for central government departments over the next few years.
That would have a knock-on effect for the executive's budget, which is largely influenced by spending changes in England.
Further cuts to some benefits are also expected to be published alongside Reeves' Spring Statement.
That could mean thousands of people in NI lose some or all of their Personal Independence Payment, a sickness and disability benefit.
In the October Budget, Stormont got an additional £1.5bn to spend for the new financial year, beginning next week.
The chancellor's plans suggested increases in public spending would moderate after that, with day-to-day public spending increasing by only 1.3% a year from 2026.
Those spending increases could now be reduced to help the government meet its self-imposed rules on taxing, spending and borrowing.
That affects Stormont as the majority of the money that it spends comes from the Treasury, in what is known as the block grant.
Gareth Lewis
BBC Wales political editor
If the slogan of Wednesday's Spring Statement is "the world has changed" then Wales will not escape the consequences – be they real world or political.
Wales has some of highest levels of health-related benefits claims in the UK and more than a quarter of a million people on Personal Independence Payments (PIPs), which is facing large cuts.
In the political world, even if there are no tax rises or major policy announcements, tomorrow could well set the direction of travel for the year to come, which ends with the 2026 Senedd election.
Decisions made by Labour at Westminster could make the party's fight to stay in charge in Cardiff Bay easier, or more difficult.
Welsh ministers have just celebrated having £1.5bn more to spend in their budget than they had initially thought, thanks to spending decisions made by the Chancellor Rachel Reeves in England.
But any squeeze on spending or rise in taxes, implemented by Labour at a UK level, could affect Labour prospects here – especially when that polling also suggests that the vote will be very close.
Henry Zeffman
Chief political correspondent
Rachel Reeves has a new mantra which you will hear again and again today: the world has changed.
What she means by that - but which diplomatic niceties prevent her from saying - is that Donald Trump became president of the United States again. Trump’s tariff spree and upending of the US approach to the war in Ukraine have complicated the UK’s economic picture in ways which are still unfolding day to day.
Whatever Reeves says today may well be overtaken in exactly one week, when the president has vowed to impose new tariffs - although their scope is uncertain, to say the least.
In some parts of government, trying to avert more tariffs on the UK and thinking about how to respond if they are imposed is being seen as a bigger task than Reeves’s statement today.
Arguably it is also evidence that the world hasn’t just changed, past tense - it is changing, present tense. That leaves Reeves open to an argument from some of her critics, including within Labour, that her self-imposed borrowing rules and tax promises should change too.
Expect Reeves to try to pre-emptively rebut some of those arguments today. She does not believe her fiscal rules are self-imposed. Her allies argue that in practice they are imposed by markets, who would take fright if the government borrowed significantly more than it already does.
Image source, PA MediaEnergy Secretary Ed Miliband, Environment Secretary Steve Reed and Health Secretary Wes Streeting leave 10 Downing Street
A short while ago, Keir Starmer's top team departed No 10 after what was presumably a pretty jam-packed cabinet meeting.
We won't get the chancellor's traditional Red Box moment - of Budget fame - as the government insists this isn't major economic event.
We haven't caught sight of Rachel Reeves yet, but we're watching and waiting for her departure from No 11 later on.
Our next sighting will come at midday when PMQs starts and she takes her spot on the government benches, next to the prime minister.
Once Starmer's done taking MPs' questions, he'll sit down and Reeves will replace him at the dispatch box to deliver her statement.
It's a busy day. Stay tuned.
Image source, PA MediaHot on their heels were Baroness Chapman of Darlington, Education Secretary Bridget Phillipson, and Transport Secretary Heidi Alexander
Image source, ReutersDefence Secretary John Healey tells BBC Radio 4's Today programme that Reeves will provide a "tough, strong statement in tough times", and will say the "world is changing". The government's task, he adds, is to "secure Britain's future".
Healey is asked why the chancellor does not alter her own self-imposed rules, which limit how much she can borrow. Remember, some European nations are borrowing more in order to increase defence spending.
"If you borrow more you have to service the cost of that borrowing, and if you borrow more, the prices go up," he says.
"There doesn't seem to be anything good on the horizon," says Malcolm Hindley, a retired window cleaner from Liverpool.
A widower, he lives with his daughter, who "does everything round the house" and cares for him and her disabled daughter.
He owns his own house but finds it hard to get by on his £200-a-week state pension, plus attendance allowance of around £80 a week.
He needs a car to get to the shops and medical appointments and has just been in a car accident that has left him with a neck brace, on top of existing mobility issues.
He will be listening out on Wednesday for further details around cuts to benefits for the long-term sick and disabled.
Losing the winter fuel payment was hard, he says, because he feels the cold more as he gets older. Now he is worried what else might go.
Kevin Peachey
Cost of living correspondent
Among all the talk of fiscal rules and economic forecasts, there is likely to be a direct impact on your finances from the Spring Statement.
We are not expecting any tax raising, or cutting, measures.
But there will be more detail on the announcements about disability and incapacity benefits.
Broader spending plans could lead to changes to local services or grants, for example.
And watch out for the launch of consultations or longer-term plans. We will keep a keen eye out for anything that potentially changes allowances on tax-free Individual Savings Accounts (ISAs), stamp duty, or pensions in the future.
The Spring Statement will start at about 12:30 UK time, straight after Prime Minister's Questions. It will be broadcast live on BBC iPlayer and here on this page (just tap the watch live button above).
We'll bring you live updates and analysis in the lead up and throughout
Faisal Islam
Economics editor
UK long-term government borrowing costs continued to rise on Tuesday in a sign of the pressure Chancellor Rachel Reeves is under. New official economic forecasts will be revealed today alongside details of welfare cuts and a new squeeze on departmental spending.
The emphatic message from No 11 is that the Spring Statement is not a Budget but is a continuation of the chancellor’s existing strategy. There will be no Red Box, no tax changes, instead only a small table of new policies, meant to correct a gap in the public finances.
The biggest single move was already announced last week when the government outlined a £5bn cut to working-age welfare benefits. Although, since then, it looks like Reeves will have to make steeper spending cuts after being advised her reforms would not save as much as first hoped.
The forecast from the Office of Budget Responsibility will show a weaker economy this year as well as a steep rise in interest payments on government borrowing.
It is for this and other reasons that the chancellor will resist calls to adapt her self-imposed limits on borrowing, to account for new global realities. But she will acknowledge this "changed world", and new details are expected on using defence spending to help boost a lacklustre economy.
Rachel Reeves: A strong economy depends on strong defence
There will be much talk about cuts today, but one area of government spending getting a boost is defence spending - which is heading for a £2.2bn uplift from April.
In February, the government announced it would increase spending on defence to 2.5% of GDP by 2027, with an "ambition" to reach 3% after the next general election.
It announced at the time it would be cutting the aid budget from 0.5% of gross national income to 0.3% in 2027 to fund the defence increase.
In her statement to the Commons today, Reeves will say the increase in defence spending is "not just about increasing our national security but increasing our economic security, too".
But some economists argue the increase in defence spending will have a limited impact on economic growth.
Some analysts have pointed out that defence spending is more capital intensive than aid spending, meaning more of it is exempted from the chancellor's self-imposed borrowing rules.
Dharshini David
Deputy economics editor
The chancellor has been backed into a corner by her own rules - and economic circumstances.
Those rules, designed to maintain credibility and keep a lid on government borrowing costs - say that in five years, day to day spending (on items such as welfare and public services) has to be matched by income. In other words, taxes.
But as she injected large amounts into public services in the October Budget, the chancellor met the rules with a slim margin to spare - £10bn, or less than 1% of government spending.
And the economy is easily knocked off course. The growth outlook is weaker than in October, partly, some economists say, the result of the chancellor's own tax rises. This means less money for the public purse than hoped.
Government debt repayments are higher, largely the result of movements in global financial markets.
So that safety margin has likely been wiped out, and to meet her "iron clad" rules, the chancellor will trim some spending plans.
Government ministers are starting to arrive at Downing Street for a cabinet meeting, which had been pushed from Tuesday to Wednesday this week to account for the Spring Statement.
Image source, ReutersDeputy Prime Minister Angela Rayner
Image source, ReutersHealth Secretary Wes Streeting
Image source, ReutersDefence Secretary John Healey
Image source, ReutersBusiness and Trade Secretary Jonathan Reynolds
Henry Zeffman
Chief political correspondent
Here’s one way in which the world has changed: today was not meant to be a big deal.
As part of a commitment to give businesses and consumers the certainty of only one major fiscal event a year, the government had downgraded today to a “spring forecast”.
The plan was that Rachel Reeves would formally note that the Office for Budget Responsibility (OBR) had produced new estimates about the state of the economy now and over the coming years, but little more than that.
It is now much more significant: one of the big moments in the life of this government for it to demonstrate economic grip. Terminologically, it has been upgraded from a spring forecast to a Spring Statement.
But while it has become significant it is not a Budget. We are not expecting the kinds of changes to tax policy in all walks of life that often take place in a Budget.
And it is just one of several significant moments hurtling towards Reeves, most notably the spending review on 11 June at which she will confirm how much money each government department will have for the next three years.