Theresa May is battling to save her Brexit strategy as negotiations with the European Union remain “deadlocked”, amid warnings that the Prime Minister is heading for another crushing defeat in Tuesday’s crunch Commons vote.

Tory Brexiteers said rejection of the Withdrawal Agreement is “inevitable” unless Mrs May is able to secure significant changes to the Northern Ireland backstop.

“Technical” talks between officials took place in Brussels over the weekend and the PM spoke to European Commission president Jean-Claude Juncker on Sunday night.

But a Downing Street source said the negotiations remained “deadlocked”.

A plane was reported to be on stand-by at RAF Northolt to fly Mrs May to Brussels to clinch an agreement if there was any sign of a deal after talks over the weekend.

Some senior Conservatives said on Sunday that the PM should postpone the “meaningful vote” rather than risk another damaging reverse.

Instead she was being urged to table a “conditional” motion setting out the terms for dealing with the backstop issue which Parliament would be prepared to accept.

Jacob Rees-Mogg, chairman of the pro-Brexit Tory European Research Group, told the Times that it “would not be a foolish way to proceed”.

He added: “I think a meaningful vote with an addendum saying this House will support a deal if such and such is done might be a way of uniting the party or limiting the scale of the defeat.”

Former chief whip Andrew Mitchell told the paper: “Anything that avoids what looks like a massive defeat on Tuesday is worth considering.”

Meanwhile, Public Health Minister Steve Brine has warned that he will resign unless Tory MPs are given a free vote in a vote expected later in the week on whether Britain should leave the EU without a deal.

“I think a free vote would be very smart,” he told BBC Radio 4’s The Westminster Hour.

“I would find it very difficult, actually impossible to be part of a policy that was pursuing actively no-deal.”

Tory MP George Freeman said Mrs May should quit after Brexit, telling the Radio 4 Today programme: “I hope the Prime Minister can get withdrawal through and then I do think we need to choose a new leader for a new generation with a new vision of a conservativism that can make sense of Brexit and reinspire and reunite the nation.

“I hope we can do that having secured a sensible Withdrawal Agreement. A panicked change of leader now will solve nothing, we have got to get this through.

“I hope colleagues this week will recognise that: vote for the deal and then we can change.”

Environment Secretary Michael Gove – one of the leaders of the official Leave campaign in the referendum – became the latest Cabinet minister to urge MPs to vote for Mrs May’s deal.

In an article for the Daily Mail, he said: “I hope that everyone who believes in our democracy – in the importance of delivering Brexit, but also in the critical need to unite our country – will come behind the Prime Minister’s deal this week.”

The calls for a postponement came after former Cabinet minister Nicky Morgan warned that Mrs May’s position would become untenable if Parliament “dismantled” her Brexit policy in a series of votes during the course of the week.

Nevertheless, delaying the meaningful vote would be another humiliation for the Prime Minister after senior ministers spent the weekend insisting it would go ahead as planned.

Mrs May had already postponed it once from December, only to see it resoundingly defeated the following month by a majority of 230.

With less than three weeks to Brexit Day on March 29 – when Britain is due to leave the EU – any delay would raise renewed questions as to whether there was any way she could get her deal through the Commons.

Mrs May has said if she loses the vote on Tuesday, there will be further votes on Wednesday on whether the UK should leave with no-deal and on Thursday on whether they should seek an extension to the Article 50 withdrawal process.

Many at Westminster believe that in that event MPs would vote to delay Britain’s departure – to the fury of Brexiteers.

Gavin Cordon is Press Association Whitehall Editor.