THERESA May has insisted her Chequers blueprint is the “only credible” plan for Brexit and made clear she would “never accept a second referendum” on EU withdrawal.

As the Prime Minister promoted her compromise proposals over dinner with fellow European leaders at an informal summit in Salzburg, Carwyn Jones, the Welsh First Minister, intervened, arguing that if Holyrood and Cardiff were to oppose the final Brexit deal, then there should be a general election, which could eventually lead to another EU referendum.

"The next step is to see whether a deal can be supported by, for me, parliaments plural: Westminster; Edinburgh and Cardiff. If that doesn't happen, then I don't see any alternative other than a general election where Brexit would be the main issue.”

The Bridgend AM added that if there were an inconclusive result at an election, then there would be “potential for a second referendum".

When asked if the Scottish Government agreed with Mr Jones’s point about a potential general election, a spokesman for Michael Russell, the Constitutional Affairs Secretary, replied: “The Scottish Parliament has already rejected Brexit and we will make sure that Holyrood has the chance to continue to make its voice heard as the Tories drag us close to the cliff edge of a no-deal or a blind Brexit.

“It simply should not come down to a choice between those options: the catastrophic or the merely disastrous,” he added.

Before the Salzburg dinner began at the Felsenreitschule - the theatre made famous by the von Trapp family in the film The Sound of Music – Mrs May insisted her Brexit blueprint 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 stressed: "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."

But ahead of the dinner Donald Tusk, the European Council President, made clear the UK’s Brexit plans needed to be "reworked".

Announcing a special EU summit in mid-November – which will set the scene for signing any Brexit agreement – Mr Tusk said that while there was “more hope” a deal would be done, there was “less time” in which to do it.

Today, David Davis, the former Brexit Secretary in a speech in Munich will insist the Chequers Plan was “always a non-starter” and he and his fellow Brexiteers would “shortly be presenting an alternative plan which will outline a more ambitious vision".

On her arrival in Austria, the PM welcomed how Michel Barnier, the EU’s chief negotiator, had recognised his original plan for the Irish border was unworkable and had sought to come up with an “improved” solution. But Whitehall sources made clear that the private suggestions about Brussels's new proposals were unacceptable as they still did not drop the view that Northern Ireland could be treated as a separate customs jurisdiction from the rest of the UK.

Mrs May stressed: “What we cannot accept is seeing Northern Ireland carved away from the UK customs territory because, regardless of where the checks would be, what that would mean would be that it would be a challenge to our constitutional and economic integrity."

She also decried “prominent Labour members like the Mayor of London,” who were now trying to take Britain “back to square one” with support for a People’s Vote on Brexit.

"I want to be absolutely clear, this government will never accept a second referendum,” declared the PM, adding: "We held a People's Vote; it was the referendum in 2016.

“People voted to leave the European Union, it is now a matter of trust in politicians that we should deliver on the vote of the British people," she added.

Earlier, Lord Steel, the former Liberal leader, urged the PM to make a television broadcast to call off Brexit and announce a second referendum.

“In the words of the popular American song,” he added, “let’s call the whole thing off.”

The intervention by the former Holyrood Presiding Office came after a People's Vote report, written by fellow Scottish peer Lord Kerr of Kinlochard, who authored Article 50, suggested Mrs May could be forced to concede a second referendum by a vote of MPs or that she could even decide to call one herself. It stressed the option of staying in the EU "must be on the ballot paper".