Updated 16:20

The British Prime Minister Theresa May is heading for a defeat on the UK's Brexit vote in the the House of Commons.

Senior MPs are predicting a defeat for Mrs May of between 100 and 200 votes, which is likely to be followed by British Labourt leader Jeremy Corbyn calling a vote of no confidence in the British government.

Mrs May's allies insist that whatever the scale of the defeat she has no intention of quitting or calling a general election, but she will come under enormous pressure to unveil a Brexit plan B.

On the eve of the historic vote, she appealed to MPs during a Commons statement to take a "second look" at her agreement, despite admitting it was not perfect and was a compromise.

Then she urged them to "keep Jeremy Corbyn as far away from No. 10 as possible".

Winding up day four of the five-day Commons debate on the withdrawal agreement, the British Chancellor Philip Hammond told MPs: "We as a House now need to move swiftly and decisively to get behind the deal.

"To make the tough choices that are needed to simultaneously deliver the Brexit people voted for, to protect our economy and our national security and to give them the brighter future they were promised."

Mrs May's final appeal to MPs to back her deal will come amid what is certain to be an atmosphere of tension and high drama, as she winds up the final day of the debate - before voting begins at 7.00pm.

However, MPs will first vote on a series of four amendments.

The amendments include opposition motions - with Labour's Jeremy Corbyn's motion calling for the rejection of Mrs May's deal, a "no-deal" Brexit to be ruled out and for MPs to instead back Labour's plans for a permanent customs union.

However, the amendments also include ones from Tory Brexiteers - including one calling for the UK to be given the explicit power to terminate the backstop without permission from the EU.

Mrs May is expected to make a statement immediately after the vote - and is likely to pledge to go back to Brussels to try to win legally-binding guarantees on the Irish backstop.

But opposition leaders, with the support of remainers, are likely to call on her to delay the UK's divorce from the EU by asking for an extension of the Article 50 process.

The EU has repeatedly ruled out the prospect of any fundamental changes to the withdrawal deal, and will likely reject any efforts to water down the Irish backstop plans.

However, senior EU officials - including Tánaiste Simon Coveney - have indicated they'd be open to considering a request for an extension of Article 50.

"We ask you to reconsider"

Meanwhile MEPs have signed a letter to the British public, asking them to reconsider their decision to leave the bloc.

The message, organised by Austrian MEP Josef Weidenholzer and signed by 129 colleagues, says they believe there is support for a second referendum as they have "growing anxiety at the unfolding of Brexit disaster".

It says: "We are reluctant to intervene in your domestic politics, but we cannot help but notice that the opinion polls show a growing number of voters who want an opportunity to reconsider the Brexit decision, now that it is clear that Brexit is very different to the promises made by the Leave campaign nearly three years ago."

The representatives, including people from the conservative, liberal, socialist and green groups, say: "Any British decision to remain in the EU would be warmly welcomed by us and we would work with you to reform and improve the European Union, so that it works better in the interests of all citizens."

The letter says the EU has benefited from contributions by Britain from both its people and politicians.

The letter goes on: "Indeed, should the UK decide to withdraw the article 50 letter received by the President of the European Council, then we as members of the European Parliament would support it.

"We have greatly appreciated the enormous impact British politicians and citizens have contributed to the European project over the last 40 years. We would miss the extraordinary expertise of our British colleagues.

"We ask you to reconsider to leave our Union in the interest of the next generation of young people, British and Europeans, who will lose out on the opportunities of living, loving and working together. Brexit will weaken all of us.

"We want you to stay. Together, we are stronger and together we can build a stronger Europe."