The United Kingdom will not be able to agree “a halfway house” with the European Union that will significantly improve its fortunes, the UK’s former top diplomat to the EU has declared.

Speaking in Dublin to mark the 10th anniversary of Brexit, Ivan Rogers said he brought “little good news” and that he sees little prospect that the UK could rejoin the EU.

The UK’s economic health “hasn’t been improved by Brexit, that’s self-evident and it would today be better off” if it had remained in the European Union, said Rogers, the former UK permanent representative to the union.

Exiting damaged the economy and tax revenues, he said.

“That then leads to further pressures on public services and defence spending and everything else, because you’ve got less money to spend,” he told a conference organised by the European Commission’s Office in Ireland.

“So, that exacerbates the issues that we were already feeling before we left, and it’s made them harder to fix, not easier.”

He added: “Brexit is as much a symptom of this malaise, not solely a cause of it. The United Kingdom’s economic performance has been pretty grim. Productivity has been pretty weak for a sustained period.”

British politicians, he said, “are bending over backwards, and have now been for a very long time, not to relitigate Brexit and not tell the public that they were fools to have voted for it”.

Its supporters argue that Brexit gave “an opportunity to fix the UK’s endemic problems,” but the opportunity was “squandered” by those trying to frustrate the 2016 referendum’s outcome.

Rogers said he did not agree with this view and that Brexit made it “more difficult to tackle problems, not easier”, precisely because it damaged trade links with the UK’s nearest neighbours.

He said it has “become endemic” for some to believe the UK can “cherry pick what we like” about the EU, while “still having a warmer relationship with the US, with China, with India than anybody else”.

The “brilliance of the Brexiteer campaign” was that it persuaded a majority of voters that their “fantasies of what was wrong about the world” could be corrected by Brexit.

Different visions of life after Brexit were promoted by Brexiteers, such as the “globalist, free-trading, buccaneering, bold mid-Atlantic” version offered by Lord Daniel Hannan.

“Remember, ‘Let’s Go WTO?’ Remember all that nonsense? How does that look 10 years on? Not terribly healthy, really,” Rogers said.

Reform leader Nigel Farage had, Rogers said, offered “a chauvinist, nativist, and sometimes rather worse than nativist, Brexit”, trumpeting the false threat posed by 76 million Turkish people allegedly wanting to come to the UK.

He said Farage – “the most significant UK politician in the last 15 years, though he has never held office” – was most responsible for Brexit, but his party has led in “every one of the last 300 opinion polls”.

A third of UK voters believe they were misled in advance of the referendum 10 years ago, including a lot of Reform voters, “yet they do not think it’s solely the fault of the Tory establishment that they were mis-sold”.

Today, Rogers said, Farage “is back with a different version of a popular populism built primarily around migration and small boats, and asylum seekers”.

Rogers added: “He doesn’t mention Europe very much any more, that’s no longer his agenda.” And Rogers noted that most people believe 40 per cent of asylum seekers arrive by small boats, but the actual figure is 4 per cent.