Julian Smith, the Northern Ireland secretary, was in Downing Street yesterday as fraught negotiations over the deal continued

Senior figures in the Democratic Unionist Party attacked Boris Johnson’s deal yesterday as “not Brexit” in a effort to convince Conservative MPs to join them and vote it down.

Sammy Wilson, one of the party’s MPs, called on Tories to “take a stand” against something that would “drive a coach and horses” through the Good Friday agreement.

The architects of the 1998 peace accord were split yesterday on the impact Mr Johnson’s deal would have on Northern Ireland. Sir John Major, the former prime minister, and Jonathan Powell, Tony Blair’s former chief of staff, said that it could lead to the break-up of the United Kingdom.

Mr Powell says in a letter to The Times today that Mr Johnson may “have done more to