Adopting Boris Johnson’s Brexit plans would leave the Conservatives’ commons majority at risk of collapse after their Northern Irish DUP partners branded the proposals too “vague”.

The party’s Brexit spokesman Sammy Wilson said a Canada-style trade deal advocated by Mr Johnson and other Brexiteers was 'not something we could support'.

It comes as ex-foreign secretary Mr Johnson set out how he believed such a plan might work in a sprawling 4,600 word article on the eve of conference.

But the DUP’s stance is a boost for Ms May as she attracted criticism from all wings of her party over a lack of vision for the UK.

Mr Wilson told the Belfast News Letter that the proposals for a Canada-like free trade deal, with added elements, set out in a paper by Brexiteers David Davis and Jacob Rees-Mogg were “inconsistent”.

He said: “I am not sure if this report is deliberately vague or just not very well thought out.

“It talks about the goods which are regulated differently in EU member states, and uses the phrase 'of which there are many’.

“Are they saying that the UK government would commit to, or the NI Executive would be required to commit to, copying all of the EU regulations in relation to that myriad number of goods? That is not clear.”

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Mr Wilson, who has also been critical of Ms May’s plans, went on to raise doubts about laws for some goods being specific to Northern Ireland rather than the whole UK.

In his article advocating his proposals, Mr Johnson accused the government and civil service of a “pretty invertebrate performance” in negotiations and said there had been “a collapse of will by the British establishment to deliver on the mandate of the people”.

The former mayor of London said Ms May’s proposal would leave the UK “half-in, half-out” of the European Union and proposed a six-point alternative plan for Brexit.

Within that he argued for a new withdrawal agreement in which the Irish border question would be settled as part of the deal on the future economic arrangements.

Elsewhere, Tories across the party turned their fire on the prime minister ahead of its Birmingham get together, warning her that the they risk being "stuck in political rhetoric of the past".

Senior figures have been rattled by the interventionist policies set out at the Labour conference, which have attracted attention away from rows over Brexit and antisemitism.