Conservative MP Dominic Grieve's amendment (g) would suspend Standing Order 14(1) (which gives government business priority) on six days.

On each of those days a motion saying that the House has considered the UK’s departure from, and future relationship with, the EU will be first item of business. Although the motion will be ‘neutral’, the relevant Standing Orders will not apply so that it will be amendable by MPs.

After six and a half hours, amendments will be voted on before the motion itself.

What does this mean?

The amendment would force the government to make time for MPs to discuss a range of alternatives to the prime minister's Brexit plan on six full days in the Commons before 26 March.

MPs would be able to table amendments to be voted on at the end of the debate, which could include alternative Brexit options such as Labour's plan, a second referendum, no deal and the Norway-style relationship preferred by some MPs.

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Tory MP Dominic Grieve speaks for his amendment (g), which aims to give MPs the opportunity to debate and then vote on alternatives to the PM's deal over six days.

He says Parliament is in a position of "complete paralysis", with the government attempting to place an "absolute straitjacket" on MPs.

The amendment aims to reach some conclusion that a majority can support.

The prime minister's suggestion that his proposal is some sort of "constitutional abomination...does not bear scrutiny", he adds.

One thing that there is a majority for is against a no-deal Brexit, he says, and as result he will back the amendments that seek to prevent that.

He says he cannot support the Brady amendment as it does not reach a conclusion. He's glad however that his previous amendment - that made motions amendable - has had some effect.

Amendment (n), or the Brady amendment, is an amendment proposed by senior Conservative backbencher Sir Graham Brady.

Believed to have the backing of a large number of Tory MPs, including former ministers, the amendment calls for Parliament to require the backstop to be replaced with “alternative arrangements to avoid a hard border” but would otherwise support the prime minister’s deal.

Pro-Brexit Tory MPs are currently meeting with the government's chief whip Julian Smith, the BBC understands.

The MPs will discuss whether they will support an amendment to replace the planned Irish backstop with "alternative arrangements", the BBC's chief political correspondent Vivki Young reports.

The government hopes the amendment, tabled by Tory MP Sir Graham, could win the support of Conservative rebels and help pass a version of Theresa May's deal.

Members of the Euroscpetic European Research Group (ERG) are also expected to meet among themselves at 18:00 GMT - about an hour before MPs vote on the amendments.

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Former Tory leader Iain Duncan Smith accepts the challenge that "now we have to say what we are in favour of".

However, he says he opposes delaying Brexit and is also opposed to the backstop.

He says discussions in the last 24 hours have indicated a willingness to reach agreement amongst Conservative MPs, urging colleagues to "strive towards finding some kind of compromise".

He supports the Brady amendment, he says, "not because I give a blank cheque, but because I believe it is necessary for us now to send the prime minister back [to Brussels] with a full wind."

None of the amendments proposed, if successful, would be binding on the government, although support for any of them would put political pressure on Theresa May to follow their direction.

However, if Yvette Cooper's amendment is successful, and she then managed to get MPs to approve her bill, it would become law and so place an obligation on the government.

She is trying to rule out the UK leaving the EU without a formal deal by allowing Parliament time to pass a new law.

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Labour's Yvette Cooper is introducing her amendment, which would provide the ability to Parliament to vote for an extension to Article 50.

She says "there are two months to go" until the end of Article 50. She states that the PM's deal was rejected because it was a "blindfold Brexit that weakens our negotiating hand".

She warns that the "chasing of unicorns" could leave the UK with "no-deal by accident". And she says that when she voted to trigger Article 50, she called for a "cross party commission" to be formed to examine the next Brexit outcomes and potentials.

She warns that "chaos and division will get worse" if no-deal is actually allowed to happen.

Five months were used for a general election of the 24 month Article 50 timeline, while 22 months were spent before a deal was presented to Parliament, she adds.

"Saying the same things again and again" will make it more important that her amendment, providing a "safety net" is agreed to, she states.

A Labour MP who had hoped to ask about the possibility of a new referendum on the UK's EU membership has hit out at party leader Jeremy Corbyn.

Angela Smith says the leader of the opposition's refusal to allow her to intervene with a question about a so-called People's Vote during this afternoon's debate was "against the spirit' of the House of Commons.

The Labour MP retweeted this from Business Insiders senior political reporter Adam Payne:

Daniel Sandford
Home Affairs Correspondent

The blood donation service has been telling some social media users that it will not hold blood donation sessions in Dover or Folkestone just before and after Brexit.

In reply to some users, @GiveBloodNHS wrote: "We have taken the decision to cancel blood donation sessions in Dover and Folkestone for a two-week period before and a six-week period after Britain's exit from the EU.

"This is because in the event of issues in Calais and other freight ports, this could lead to significant traffic in Kent and may prevent donation teams from reaching or leaving venues in the area.

"We will hold replacement sessions at other locations and we will still be in a position to provide the necessary blood to hospitals."

MP and former Conservative leader Iain Duncan Smith earlier told the BBC that "there is a Conservative WhatsApp group which pretty much most of the Conservative Party of all views on this are on".

"It exploded last night with a desire to come together and I think this is the main bit for the government to take away - ordinary backbenchers said we can compromise around this agreement."

Meanwhile, Steve Baker - who is backing a plan for Brexit called the Malthouse plan, which has been put forward by many Conservative MPs - said there were signs of "overwhelming convergence" around the plan on the Tory WhatsApp group.

The proposal drawn up by rival factions would extend the transition period - during which the UK would continue to follow EU rules and pay into its budget - from the end of 2020 to December 2021, to allow more time to reach a free trade deal.

Rob Watson
BBC World Service political correspondent

It’s an astonishing, critics might say desperate, development.

Two months to go until Brexit day Theresa May has said she is prepared to ask the EU to renegotiate the treaty on Britain’s withdrawal.

It’s something that until now she said was impossible.

She wants any renegotiation to focus on changing the arrangements for avoiding a hard border in Northern Ireland.

In the next few hours, MPs will vote on whether to support her new approach.

If they do, she will effectively then be betting on the EU to compromise to get her out of the UK’s most profound political crisis in decades.

The BBC's political editor says politicians on all sides are suspicious about why MPs might be backing certain amendments.

One political journalist tweeted, external that he was told by one Brexiteer that "backing Brady buys us another few weeks... then we can just vote the deal down again in Feb".

Conservative MP Nick Boles retweeted the tweet, and said this was the "real agenda" of the European Research Group - the group of Eurosceptic backbenchers.

Theresa May has faced a backlash from MPs, with several ministers resigning in protest at the backstop proposals included in the withdrawal agreement.

The DUP wants the government to "bin the backstop". Their MPs have repeatedly said they would not accept any additional Northern Ireland-only checks, saying any differences between NI and Great Britain could threaten the union.

However, it has been urged by business and agri-food groups in Northern Ireland to support the government's plan.

Brexiteers in other parties also expressed concerns about the backstop, fearing the UK would continue to follow EU rules for an indefinite time without having any say over them, with no way of leaving without the EU's agreement.

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The SNP's Westminster Leader Ian Blackford says Westminster is "now taking powers" from the Scottish government against their will.

"Scotland will and must have the right to determine its own future," he declares.

He says that the vote on the immigration bill "is the latest" instance of Westminster voting against Scotland's wishes.

"This place wants to slam the door shut and pull up the drawbridge" on entry to the UK, he says.

"The UK government has ignored the views of the people of Scotland," he adds.

He says that the SNP will "continue to vote down" the "blindfold Brexit" which would drive the UK "off a cliff".

"She cannot even control her own disunited party," he adds, "they should all hang their heads in shame."

Tory backbencher Sir Graham Brady has tabled an amendment to the Brexit deal which calls for the planned Irish backstop to be replaced with "alternative arrangements".

The government was hoping this could win the support of pro-Brexit Conservative rebels and help pass Theresa May's deal.

According to Reuters, Theresa May spoke to the president of the European Commission, Jean-Claude Juncker, before making her statement to Parliament.

BBC News Channel

Conservative MP Robert Buckland, who is also the Solicitor General, says the PM has "trumped" Yvette Cooper by promising to make a statement on the next steps for Brexit by 13 February - if no new deal is reached.

Ms Cooper's amendment is calling for a new bill to delay Brexit in order to allow more time to reach a deal. Her amendment would mean that if by 26 February Mrs May's deal is not approved by MPs, Mrs May must seek to extend Brexit day (29 March).

Mr Buckland said: "I think that should give all of us who are concerned about the clock running down the necessary certainty and comfort that we will be able to take action at the appropriate moment."

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"What is the vague alternative to the perfectly acceptable backstop?" Tory MP Ken Clarke asks, criticising the Brady amendment.

Independent MP Lady Hermon is the only Northern Irish MP "who agrees with the majority of the Irish population", he says, pointing out that she supports the “perfectly harmless” backstop. He says it is "absurd" to reopen the issue.

He adds that he will support anything which extends Article 50.

"We need more time," he says.

Vicki Young
Chief Political Correspondent

Theresa May is actually saying to her own MPs, I want you to back an amendment from a Conservative that goes against what I've negotiated with the EU over the last two years.

It's quite an extraordinary position to be in, but then again it was an extraordinary defeat that her deal suffered two weeks ago.

We haven't really heard much from Theresa May in the last couple of weeks about what her plan B is. She has been forced by various parliamentary shenanigans to come to the House today and she has made it clear now that she's going to go back to the EU and say 'I want you to reopen the withdrawal agreement', something they have said all along that they can't do.

As far as the EU are concerned, this deal has been signed off.

What she is saying to Parliament is that we can't keep showing people what we're against, it's time we showed them what we're in favour of. So if the problem is the backstop, if it's the problem that we can't get out of it unilaterally or it needs to be time limited, then we need to tell the EU that and it's clear she's going back to them them and will ask them to compromise.

I suppose she has no other choice at this point. With only two months to go until we leave, she has to show that she has tried.

There's been an awful lot of frustration on the side of the Brexiteers in her own party who feel that she should have ages ago gone to the EU and said 'look this isn't going to get through Parliament, you need to compromise' but that now is what she's going to do.

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Father of the House, Tory MP Ken Clarke, says this is an "enormously unique political crisis" that takes two forms: MPs are attempting to break political deadlock, but also facing a "constitutional crisis" about the credibility of government and Parliament in its ability to reach an agreement.

The public are looking at the political system "with something rather near to contempt", he says, "and we really do need to settle down...in deciding how we're going to come to conclusions about the way forward."

Today's debate is only happening because the government resisted the whole idea of coming back to MPs on the Brexit deal and "that has worried me all the way through", he says.

However, he suggests the prime minister has indicated today that she is taking a different approach, and whatever happens next will be bought back to MPs for their approval.

If a clear wish is expressed then the government will consider itself bound to follow the wishes of MPs, he suggests. In that case, there is a much bigger responsibility on MPs to reach a consensus.