Theresa May’s 27 European counterparts will consider the next stage of the Brexit process after she told them her Chequers plan was the only credible route to a deal.

The Prime Minister set out her blueprint over dinner with fellow leaders in Salzburg after being told by EU chiefs that significant elements of it would have to be reworked.

However, at the gathering in Austria, Mrs May insisted there would be no delay to the UK’s March 2019 departure, no second referendum and therefore the onus was on the continent’s leaders to find a solution if they wanted to avoid a no-deal Brexit.

Scottish First Minister Nicola Sturgeon has reportedly written to UK opposition leaders calling for them to back an extension to Article 50 if no deal is reached and warned the PM against taking the country “off the Brexit cliff edge”.

In Mrs May’s absence on Thursday, the 27 other EU leaders will discuss issues including the UK’s future relationship with the EU and how to resolve the problems around the Irish border.

European Council president Donald Tusk identified both as areas where the UK’s proposals would need to be “reworked”.

But Mrs May said Chequers was “the only credible and negotiable plan on the table that delivers no hard border in Northern Ireland and also delivers on the vote of the British people”.

She added: “If we are going to achieve a successful conclusion then, just as the UK has evolved its position, the EU will need to evolve its position too.”

UK Government sources revealed that Mrs May used Wednesday night’s dinner to acknowledge the difficulties and that she had “never pretended Brexit would be easy or simple”.

She made clear the high stakes of the negotiations over the coming weeks if a deal is to be struck this autumn in time for ratification ahead of March 29, 2019 Brexit day.

Brexit graphic
(PA Graphics)

A senior UK official said her message to them was “we all recognise that time is short but delaying or extending these negotiations is not an option”.

She said: “I believe that I have put forward serious and workable proposals.

“We will, of course, not agree on every detail, but I hope that you will respond in kind. The onus is now on all of us to get this deal done.”

In a signal that the UK would not deviate from its course, Mrs May stressed there would not be a fresh vote on the Brexit process.

“I want to be absolutely clear, this government will never accept a second referendum,” she said.

“The British people voted to leave the European Union and we will be leaving on March 29, 2019.”

Ms Sturgeon warned that it would be reckless for Britain to leave the EU without a deal in March and has written to opposition leaders urging them to back a delay if no agreement has been reached.

“Taking the UK off the Brexit cliff edge without knowing where it lands would be the most irresponsible thing any prime minister has done in a very, very long time,” she told the BBC.

“That’s why I think if that’s the situation we end up in (then) extending Article 50 is a far better way of proceeding.”

The Prime Minsiter will hold talks with both Irish premier Leo Varadkar and Mr Tusk in the margins of the Salzburg summit.

Mrs May’s approach to the Brexit negotiations received fresh criticism at home while she was in Austria from one of her former supporters.

Sir Mike Penning, a former defence minster who voted Leave before backing Mrs May for the party leadership in the aftermath of the referendum, told the Telegraph she had treated Tory MPs “like children who belong on the naughty step”.

The former soldier told the paper he was joining the hardline Brexiteer European Research Group (ERG), saying: “I’ve come to the conclusion that this ‘put up, shut up’ attitude of the Prime Minister’s – it’s Chequers or nothing – you do as you’re told or else, is a massive insult, not only to my colleagues but also to the voters.

“She is playing a game of Russian Roulette with the country which is frankly an insult to the referendum result and all those people who voted, no matter how they voted.”