"If I were the chancellor, it would be keeping me awake at night." So says Paul Johnson, director of the Institute of Fiscal Studies, who thinks George Osborne's Budget plans look increasingly at the mercy of a further downturn in Britain's growth prospects.

 "If there was another downgrade in fiscal forecasts of a similar magnitude and the chancellor did wish to remain on course... then this would surely require more real policy change," he says. 

The Institute of Fiscal Studies is holding its traditional - and very closely watched - post-Budget briefing. Click here, external to read IFS chief Paul Johnson's opening remarks, and presentations by other IFS experts.

Conservative MP Andrew Percy has been on the World at One warning about the "wrong message" sent out by the disability cuts. Here's the interview.

IFS chief Paul Johnson says that George Osborne, who raised capital gains tax in 2010 and cut it yesterday, "is following a long tradition of confused and indecisive chancellors who can’t quite make up their minds about whether to prioritise protecting the income tax base by having a higher CGT rate or incentivising investment by having a lower rate". 

He adds: "We need a serious plan and strategy here. This is not the way to make good tax policy."

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IFS director Paul Johnson comments on George Osborne's new sugar tax:

"A tax just on soft drinks is clearly only very partial. Only around 17% of added sugar consumed comes from soft drinks – though the proportion in households with children is a little higher. Obviously the soft drinks tax won’t have any impact on the other 80+% of sugar consumption – indeed it might increase it as people move away from soft drinks to other sugary products. That said taxing soft drinks, which have little or no other nutritional value, may well make sense as a first step."

BBC assistant political editor Norman Smith tweets:

Deputy political editor James Landale tweets:

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IFS director Paul Johnson has been giving his analysis of the Budget to the World at One.  

"[George Osborne] has managed to shift quite a lot of money around so that he will be on current plans doing that in 2019/20, but he has had to do quite a lot of shuffling of money from one year to another. And he's also announced another £3.5bn of completely unspecified spending cuts in 2019 to get there. 

"The real problem for him is that he can sort of get away with this once in terms of ensuring that he meets his rule, but if we get another downgrade in growth prospect, he won't be able to get away with a similar set of actions next time."

Economics editor Kamal Ahmed tweets:

Deputy political editor James Landale tweets:

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The Institute for Fiscal Studies says an additional year of austerity will be required as a result of the Chancellor's Budget. 

Speaking on the World at One, IFS director Paul Johnson questions whether George Osborne will be able to meet his target of a £10bn budget surplus by the end of this Parliament without further tax rises or spending cuts.

Business presenter Ben Thompson tweets:

Downing Street says the government has raised the issue of the so-called tampon tax at European level and is "making good progress."

The Prime Minister's official spokeswoman said David Cameron was in Brussels today for an EU summit and this would be "an opportunity to engage on issues that matter to us."

She added that the main discussions would be about broad economic issues but the Prime Minister may have the opportunity to raise the issue "in the margins."

Earlier the Chancellor said the government was "on the verge of a deal" on abolishing the 5% VAT rate on sanitary products.

Sterling rose above $1.44 after the Bank of England kept interest rates unchanged as expected and said rates were more likely to rise than not over the next two years.

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Bank of England policymakers said sterling had been dealt a big hit by uncertainty in the run-up to the referendum on EU membership and that growth could slow, after voting unanimously to keep rates steady.

The central bank said the upcoming vote on 23 June could delay some spending decisions, though it said recent indicators suggested growth would keep the same momentum this quarter as it had at the end of last year.

The BoE reiterated that interest rates were more likely to rise than not over the next two years and that when they did the rise would be gradual, given likely headwinds.