British Foreign Secretary Boris Johnson is a “buffoon” who will “ruin” Ireland and the United Kingdom because of his determination to quit the European Union, former taoiseach, Bertie Ahern has declared.

In some of his strongest remarks yet on the Brexit negotiations, Mr Ahern urged British prime minister Theresa May to face down the Conservative Party’s strongest supporters of a hard Brexit.

“If she has 350 members and 70 of them are rebels something you have to say, what do we do with the 280, and she has to do that. If she keeps going from crisis to crisis, and listening to that buffoon, Boris - he’ll ruin us, never mind ruin them - she has to face up to that.

“If she doesn’t she can’t survive,” Mr Ahern told an audience last month at a commemoration in Athboy to mark the 20th anniversary of the Belfast Agreement , the Meath Chronicle reports.

Commenting on the Brexit talks, Mr Ahern urged Taoiseach Leo Varadkar to push for a deal on the key issues facing Ireland - including the future state of the Border - quickly, and not to leave everything go until the October EU summit.

“I’m not saying we can finish it all by June, but if we are to drag it out until the end, the British could come in the last few days with their €50 billion cheque and say, “We’re going to do this and we’re going to do that, and going to do the other.

“And they’ll say to the French and the Germans who are making the running on this, we’ve given the Irish a lot, now is the time for the Irish to move, and the pressure will come back on us,” the Chronicle reported.

“We had a deal on 15th December which people believed was cast iron. By 15th March it was a ‘ridiculous deal which no British prime minister could implement’. Now it’s a backstop if nothing else. They have no intention of doing that,” he said.

“We have been dragged through the December summit with little or nothing. Then there was the March summit, and what have we got and now when she couldn’t get the customs partnership through, she’s looking at another thing.”

Border poll

Speaking before the arrival in Ireland this week of the European Commission president, Jean Claude Juncker, Mr Ahern said Ireland still has the rest of the EU onside, but a deal must be struck in June. “If we wait till Halloween, it’ll be a bad Halloween party.”

Meanwhile, he rejected calls for a Border poll and a decision on a united Ireland by a simple majority: “It wouldn’t get you to Christmas,” he said.

“The only united Ireland will be a negotiated one - and it won’t happen in my lifetime,” he said, though he urged Fianna Fáil looking at how a united Ireland would work, and produce a proper study on how it could be done in time.

“If the British subvention to Northern Ireland was to go in the morning, we would be back in a recession worse than the one we just came out of,” he added.

“The only way it would work is when the nationalist and republican communities and a ‘reasonable’ share of the loyalist and unionist people want it - but with the unionists and loyalists totally opposed, it is ridiculous.

Paying tribute to the late Democratic Unionist Party leader, Rev Ian Paisley, Mr Ahern told of how the two had met in Dublin after he had stood down as taoiseach a decade ago, where they visited the Dáil, the Botanic Gardens, and Glasnevin Cemetery.

“And Ian Paisley walked down to my mother’s and father’s graves, and he knew they were in the republican plot, and he stood over them and said a prayer - I thought that was some twist to the guy.”

Looking back on the Good Friday talks, Mr Ahern said Tony Blair was very honourable and trustworthy: “He never tried to double cross me. Jonathan Powell (Downing Street Chief of Staff) did, twice, – once he apologised for and I ended up getting egg on my face in the other.”