Relations with Ireland will be “put in the freezer”. Boris Johnsonreturns as prime ministerwarned the architect of the Good Friday Peace Agreement.

Jonathan Powellwho was Tony Blair’s chief of staff and chief negotiator for Northern Ireland from 1997 to 2007, said it was vital to have someone “competent and capable” in Downing Street to get the talks back on track.

His comments came as Northern Ireland Secretary Steve Baker and Northern Ireland House of Commons committee chair Simon Hoare wrote a joint paper calling Rishi Sunaka a leader who could provide a “clear, workable and fair solution” to the long-running dispute with the EU over Irish border. .

The brief premiership of Liz Truss saw signs of rapprochement with Brussels by Northern Ireland ProtocolMr Baker apologized for the tone of his comments during and after the Brexit referendum.

But Mr Baker today warned that Tory Eurosceptics would “derail” the talks if the incoming leader abandons Ms Truss’s insistence that the European Court of Justice should be stripped of jurisdiction over the dispute.

Mr Baker told Sky News’ Sophie Ridge on Sunday: “Whoever wins this contest, the only policy that can be successfully implemented in Northern Ireland is the one we have and everyone needs to understand that.

“If, say, Rishi or Penny (Mordaunt) had not implemented this policy, the Eurosceptics would have brought down the government.

“There is no doubt, they have been very quiet, but the Eurosceptics really care about this issue of leaving the whole of the UK under the jurisdiction of European law.

“My colleagues and friends like Bill Cash, Mark Francois and John Redwood will not tolerate any diversion, any nonsense on this matter. So whether it’s Rishi, Penny or Boris, the same policy should follow the Northern Ireland Protocol.”

Mr Powell said recent progress on the protocol would “collapse” if Mr Johnson wins a second visit to 10 Downing Street.

“Anglo-Irish relations will go back into the freezer,” he told Times Radio. “Relations with the EU will be even worse.

“Having a competent and capable person in Downing Street who can actually do these things, to negotiate the protocol so that you can make it as acceptable as possible to the Unionists and to restore the relationship with the Irish Government is very important.

“Boris Johnson certainly wouldn’t do that.”

Mr Powell said Britain had become an “international laughing stock” under the Johnson and Truss governments.

“I think it has serious implications for our position in the world,” he told Kate McCann. “I think it has serious implications for how people see government.

“Competent government is more difficult than it seems. And I think both Liz Truss and Boris Johnson have shown that incompetent people in Number 10 can make a real mess. The restoration of competent government would be at least one good thing to come out of this leadership race.”

Northern Ireland Minister Chris Heaton-Harris said fresh elections to the devolved assembly in Stormont would be called if a new executive was not formed by October 28.

Mr Heaton-Harris told Sky News he hoped the DUP would lift its boycott of the executive, which is blocking the restoration of power-sharing institutions.

“There is a choice that people can make to stop the election, but that has to be made by the elected representatives in Northern Ireland who will return to this assembly,” Mr Heaton-Harris said.

“Without that, the Secretary of State (Secretary of State) for Northern Ireland will have to call an election this week.”