Johnson warns DUP if they pull plug on May's government it will put Corbyn in prime position to take over

Comments come after DUP spoke of confidence and supply agreement with government in the past tense when details of Brexit deal emerged

Boris Johnson has urged the Democratic Unionist Party not to walk out on its confidence-and-supply agreement with Theresa May, citing the risk it would usher in a government led by Jeremy Corbyn.

Senior DUP figures have referred to the arrangement that props up the prime minister in the past tense since the details of her Brexit deal emerged, such is their hostility to it, and leader Arlene Foster has indicated she thinks a Labour government would be preferable.

However, speaking at the DUP's conference, Mr Johnson said: “I hope that you agree that it is absolutely vital that we keep this partnership going and that we are not so complacent as to abandon the government of this country to a man whose avowed policy is to break up this country.”

He still managed to take the opportunity to savage Ms May’s proposed deal with the European Union, telling delegates the country was “on the verge of making a historic mistake".

“If we are not careful, we are going to stay in the customs union, we are going to stay in the single market, we are going to be rule-takers," he said.

Ms May has made clear there is no scope for her deal to be renegotiated. So if the DUP continue to support the Conservatives, the only way it could be changed, at least by the Conservatives, would be under a new leader.

So far, efforts to bring about a confidence vote in Ms May’s leadership of the Conservative party, led by Jacob Rees-Mogg, have not been successful.

Mr Johnson said the confidence-and-supply arrangement with the DUP had been crucial in preventing Mr Corbyn becoming Prime Minister. He also attacked shadow chancellor John McDonnell.

“He is a man who has not only campaigned for a united Ireland but who has still – to the best of my knowledge – failed to condemn the terrorist atrocities of the IRA,” the former foreign secretary added.

If the DUP vote against Ms May’s withdrawal agreement, as seems likely, but do not end their formal confidence-and-supply arrangement with her, it will heighten the prospect of the UK leaving the EU with no deal at all — something the Bank of England says will cause a significant economic shock.