DOMINIC Raab will today send his strongest warning yet to Brussels that Britain would be prepared to walk away from the Brexit talks, saying how its “willingness to compromise is not without limits”.

The Brexit Secretary’s shot across the EU’s bows comes less than a week after Labour leader Jeremy Corbyn warned a no-deal Brexit would be a "national disaster".

But with less than three weeks to go to the crunch October European Council, Mr Raab will use his keynote speech to the Conservative conference in Birmingham to rule out any deal which "locks in" Britain to the EU by membership of a customs union or the European Economic Area.

He will also reject the European Commission's proposal for a "backstop" solution to the Irish border issue under which Northern Ireland would remain part of the EU customs area.

The Secretary of State will say: "We are leaving the European Union in fact; not just in name. If we can't obtain a deal that secures that objective...if an attempt is made to lock us in via the back door of the EEA and customs union...or if the only offer from the EU threatens the integrity of our Union, then we will be left with no choice but to leave without a deal."

Restating his backing for Mrs May's Chequers Plan, Mr Raab will say: "My approach to Brexit is pragmatic, not dogmatic. Our proposals would deliver a historic agreement that provides a roadmap out of the EU and a final deal that will be good for the whole country.

"A deal that delivers on the referendum, because that's our democratic duty…that manages the risks of Brexit, because that's our responsibility…that grasps the opportunities of Brexit, because we're at our best when we're optimistic about the future.

"And a deal that protects our precious Union, because we are the Conservative and Unionist Party," he will declare.

Mr Raab’s words follow remarks from Liam Fox, the International Trade Secretary, who hit out at the EU for "taunting" the UK since its rejection of the Chequers Plan at the Salzburg summit.

The first day of conference was dominated by the party’s Brexit psychodrama with Theresa May and her colleagues defending her compromise proposals against Boris Johnson’s attack in which he branded them “deranged”.

The Prime Minister insisted her beleaguered Chequers Plan was not dead as she refused to rule out making any more compromises to secure a deal.

She sought to reject Mr Johnson’s suggestion that, as a true believer in Brexit, his “super-Canada” trade deal plan was better placed to succeed than her blueprint, by declaring: “I believe in Brexit.”

Mrs May also did not deny that a no-deal scenario would create a hard border between Northern Ireland and the Irish Republic, simply stating repeatedly that the UK Government was "committed" to ensuring that a hard border would not happen.

Ruth Davidson came to the PM’s defence, suggesting Mr Johnson’s harsh putdown of her Brexit compromise was “not wise” and called for Tory colleagues to observe a “period of silence” to give Mrs May the space to secure a deal.

Today in her address to conference, the Scottish Conservative leader will strike out again at the former Foreign Secretary and his fellow Brexiteers by extolling the Conservative virtues of pragmatism and practicality and decrying the “ivory-towered schemes of the ideological puritan”.

She will tell conference: “Here’s the truth: we can agree a Brexit deal under the Conservatives or we can risk handing the keys of Downing Street to Jeremy Corbyn. I know which one I believe is in the national interest. I stand by the Prime Minister.”

Last night, Mrs May failed to turn up at the Scottish Conservative reception or indeed any other reception in a bid, said party sources, to "save her voice" and avoid a repeat of last year’s embarrassing episode when she lost it repeatedly during her end-of-conference speech. Philip Hammond, the Chancellor, filled in for the PM at the Scots event.

Earlier, the PM unveiled a plan for a Festival of Brexit Britain to celebrate our “precious Union” planned for 2022.

And she announced plans to charge foreign home buyers in England up to a three per cent higher rate of stamp duty to stop them driving up prices in the UK with the revenue used use to tackle homelessness. Murdo Fraser for the Scottish Conservatives said the party would need to see how the plan translated into the Scottish system but said: “In principle, we would be supportive of this."