The British government is “riven by internal dissent” and lacks credibility on the UK’s withdrawal from the European Union, former taoiseach Enda Kenny has said.

Mr Kenny, in his first major public intervention since standing down as taoiseach a year ago, said he was “appalled” at what was happening in British politics.

Mr Kenny’s remarks undermine criticism of Taoiseach Leo Varadkar by pro-Brexit British Conservatives who have claimed that Brexit negotiations would be more productive if a more experienced politician like the former taoiseach was involved.

His views emerged as Mr Varadkar raised the possibility of postponing the formal date of Brexit in March 2019 if the EU and UK are unable to agree a deal before then.

“There are a number of different scenarios that could arise if we’re in a ‘no deal’ situation,” Mr Varadkar told TV3.

“For example, it is possible to extend Article 50 [the EU clause setting out a member state’s departure from the bloc] to allow more time for negotiations to take place.”

Speaking at an event in Dublin, Mr Kenny said there had been little progress since last December, when the UK and EU initially agreed to a number of issues, such as the so-called “backstop”, he added.

“The [British] government is riven by internal dissent, lacks credibility and clarity on the most serious issue in decades. Six months on from an agreement being reached in December last year, very little progress has been made,” the Mayo TD said.

“The EU continues to negotiate from a unified position. British business is afraid to speak out because of the spectre of a Labour government.”

He added: “If this matter is not dealt with, and if negotiations have not been concluded and signed off before the EU council in October, then we might have a very different outcome.”

Mr Kenny was speaking at a lunch hosted by the European Movement Ireland, which named him European of the Year. He was presented with the award by Mr Varadkar, who paid warm tribute to his predecessor.

Mr Kenny called on European Council president Donald Tusk to convene a special summit later this year to sign off on the final Brexit withdrawal treaty.

The Government has conceded that a deal on the so-called “backstop” - which guarantees no hard Border between North and South, even in a no-deal Brexit scenario - will not be completed until the withdrawal agreement is finalised in October.

Mr Kenny said the October summit would not be a negotiating meeting, adding that Britain was not represented at the European Council when Brexit was discussed.

“So if the negotiations have not been concluded before that meeting, then the European Council of 27 will meet to discuss among themselves, without Britain, and it will not be in a position to make a difference,” he said.

“This is so serious, I believe, that the president of the council, should consider either having a meeting before that meeting in October or afterwards, specifically and solely to deal with signing off and hopefully concluding negotiations on the relationship between the United Kingdom and the European Union. I say that in the context of maintaining relationships that we have with our friends across the water.”

Mr Kenny also criticised the US administration led by President Trump, among other international governments, for populism and “aggressive nationalism”.

“Across Europe and the world there is the rise of us and them [AND]the impeccable, calm logic of America or Hungary or Italy First.

“But there are still enough who know and celebrate the difference between patriotism and nationalism. How patriotism burns quietly, furiously in the human heart, how aggressive nationalism sets fire to decency, responsibility, memory, even humanity itself.”

He also spoke of the a “quantum change in geo-politics and economics” with an “emerging Russia and China” and “an America that is frequently unrecognisable”.

On the North, Mr Kenny said the EU’s declaration that Northern Ireland would be automatically readmitted to the union in the event of Irish unity proved again that the “ballot overruled” the bullet.

Mr Kenny secured such an agreement from the EU last year, and it had become known as the “Kenny text”.

It says: “The European Council acknowledges that the Good Friday Agreement expressly provides for an agreed mechanism whereby a united Ireland may be brought about through peaceful and democratic means.

“In this regard, the European Council acknowledges that, in accordance with international law, the entire territory of such a united Ireland would thus be part of the European Union.”

Speaking on Monday, Mr Kenny said it would provide an opportunity for Northern Ireland in the future.

“That opportunity, while it is not for now, is there for all to judge at some future time. It puts paid, for once and for all, to the warped mentality held by the Provisional IRA that it was possible to bomb the six counties into a united Ireland. The ballot overrules the bullet here.”