Respect the vote and back Brexit! Theresa May will clamp down on her Remainer MPs as she desperately tries to unite the Conservative party

• Prime Minister will urge Tory rebels to send a message of unity to the country
• Pro-EU MPs are threatening to vote with Labour on a string of amendments
• Amendments to EU Withdrawal Bill would do catastrophic damage to Brexit negotiations

Theresa May will today call on die-hard Remainer Tories to prove they respect the Brexit referendum result by backing her in a series of crunch votes.

The PM will urge rebels to send a message of unity to the country as she tries to reverse attempts by Peers to scupper Britain's departure from the EU.

A group of pro-EU MPs are threatening to vote with Labour on a string of House of Lords amendments to the EU Withdrawal Bill which – if not overturned – would do catastrophic damage to the negotiations.

Mrs May will tell them: 'We must be clear that we are united as a party in our determination to deliver on the decision made by the British people.'

It comes on the eve of two days of high-stakes debates in the House of Commons.

In an unprecedented show of unity, former Cabinet Ministers Amber Rudd and Iain Duncan Smith told pro-EU backbenchers to 'march in lockstep' or risk opening the door for Jeremy Corbyn.

Miss Rudd, who backed Remain, and Mr Duncan Smith, a Brexiteer, accused Mr Corbyn of 'cynically trying to frustrate the Brexit process for his own political ends'.

Ministers hope to avoid defeat on amendments which seek to keep Britain in the single market and customs union, delay the date of Brexit and tie Mrs May's hands on the Northern Ireland border.

The most damaging, which attempts to wrest control of the negotiations from Number 10 and hand it to Parliament, could remove the threat of the UK simply walking away from a bad deal and could even be used to stop Brexit altogether. But last night several Tories went public to make clear they would vote against the Prime Minister.

Former chancellor Ken Clarke suggested he would vote against the Government on at least three issues including the single market. Dr Sarah Wollaston, the chairman of the Health Select Committee, wrote on Twitter that she would try to ensure a 'soft Brexit'.

And on Friday serial rebel Antoinette Sandbach appeared to endorse an article on Twitter under the headline 'Remainers need courage to go for the kill'. Addressing the 1922 committee of Tory backbenchers today, Mrs May will say: 'The message we send to the country through our votes this week is important.

'We must be clear that we are united as a party in our determination to deliver on the decision made by the British people.'

Remainer Peers attached 15 amendments to the Bill, which puts EU legislation on the UK statute book and repeals the 1972 European Communities Act.

Ministers will attempt to overturn or amend all but one over 12 hours of debate.

Leading Brexiteer Bill Cash, the chairman of the European Scrutiny Committee, said: 'Those who are prepared to vote against the Government are also voting against the country and defying the referendum result.

'They have already voted for the Withdrawal Bill at third reading and cannot justify reversing that vote.'

Labour MP Caroline Flint, whose Don Valley seat voted two to one to leave, said any delay to leaving would mean voters taking part in EU elections next year which would be 'completely wrong'.