Theresa May has warned opponents of her Brexit deal that they risk "letting the British people down" as Labour said the prime minister faced a "humiliating defeat" in Tuesday's crunch vote.

She urged critics to give the deal "a second look", insisting new assurances on the Irish border had "legal force". She said the "history books" would judge if MPs delivered on Brexit while safeguarding the economy and security. But Jeremy Corbyn said the PM had "completely and utterly failed". And the SNP said the PM was "in fantasy land and the government should stop threatening no-deal". MPs will vote on the terms of the UK's withdrawal from the EU and declaration on future relations on Tuesday evening. Labour and the other opposition parties will vote against the deal while about 100 Conservative MPs, and the Democratic Unionist Party's 10 MPs, could also join them. Both May and Corbyn met their backbenchers after the PM's Commons statement on Monday night - the PM to appeal once more for their support and the Labour leader to reiterate his plan to call for a general election if the deal is rejected. Corbyn also told his MPs a no-confidence vote in the prime minister would be "coming soon", according to BBC political correspondent Iain Watson. Assistant whip Gareth Johnson has become the latest member of the government to quit his job over the deal, saying in his resignation letter to the PM that it would be "detrimental to our nation's interests". He added: "The time has come to place my loyalty to my country above my loyalty to the government." Ahead of the vote, May briefed MPs on the controversial issue of the "backstop" - the fallback plan to avoid any return to physical Northern Ireland border checks. She said her "absolute conviction" was that the UK and EU would be able to finalise their future relationship by the end of 2020, meaning the backstop would never be needed. She published a joint letter from European Council President Donald Tusk and European Commission President Jean-Claude Juncker in which they stressed their "firm commitment" to working towards such an agreement - and said if the backstop were to be used it would be for the "shortest possible period". However, they said they could not add anything to change the terms of the deal negotiated with May. The PM told MPs: "I say to members on all sides of this house, whatever you may have previously concluded, over these next 24 hours, give this deal a second look. "It is not perfect, but when the history books are written, people will look at the decision of this House tomorrow and ask 'did we deliver on the country's vote to leave the EU, did we safeguard our economy, security or union or did we let the British people down'." Five Conservative Brexiteer MPs who have been critics of the withdrawal agreement have now said they will support the government in the vote on Tuesday, including Sir Geoffrey Clifton-Brown and former Public Accounts Committee chairman Sir Edward Leigh. But former Labour leader Ed Miliband said the PM must make the government "the servant of the House" if the deal was rejected, giving Parliament an "open and honest process" to express their will. (BBC)