Commission chief Jean-Claude Juncker, and his head of cabinet, Martin Selmayr, attacked Boris Johnson on Thursday (26 May), a leader of the campaign to convince UK referendum voters to leave the EU.

Juncker and Selmayr are in Japan for a meeting of G7 ministers. Former Mayor of London and Tory MP Johnson is on the campaign trail in Britain, and recently compared the EU to Adolf Hitler.

Johnson, a former Brussels correspondent for The Telegraph newspaper, has also made the hotly disputed claim that the bloc costs the UK £350 million a week – a figure that does not include the rebate, or any EU spending in Britain.

Juncker told reporters, “I am reading in British papers that Boris Johnson spent part of his life in Brussels. It is time for him to come back to Brussels, in order to check in Brussels if everything he is telling the British people is in line with reality – I do not think so.”

That was swiftly followed by an incendiary tweet from Martin Selmayr, which appeared to compare Johnson to controversial US Presidential candidate Donald Trump, French National Front leader Marine Le Pen, and Beppe Grillo, founder of italy’s populist Five Star Movement.

#G7 2017 with Trump, Le Pen, Boris Johnson, Beppe Grillo? A horror scenario that shows well why it is worth fighting populism. #withJuncker — Martin Selmayr (@MartinSelmayr) May 26, 2016

Crumbling wall of silence

The twin salvos are the latest evidence that the European Commission’s carefully constructed wall of silence around the 23 June referendum is crumbling less than a month before the vote – particularly when it comes to Johnson.

Comparing the bloc’s supposed goal of a European superstate to Hitler’s plans for world domination appears to have stung EU bosses into speaking out.

“Napoleon, Hitler, various people tried this out, and it ends tragically. The EU is an attempt to do this by different methods,” Johnson told the Sunday Telegraph.

On Monday (23 May), UK Commissioner Jonathan Hill said at a speech at the London School of Economics, “Might I gently suggest that the best way to warm up the people with whom Britain would in future be negotiating in these vitally important talks isn’t to compare their ambitions with those of the Third Reich?”

UK Commissioner wades into Brexit debate UK Commissioner Jonathan Hill has warned that Britain’s ‘Brexit’ from the EU would put London’s status as the bloc’s pre-eminent financial hub at risk.

European Council President Donald Tusk had earlier branded Johnson’s comparison an “absurd argument”.

“Boris Johnson crossed the boundaries of a rational discourse, demonstrating political amnesia,” said Tusk, who added there was, “no excuse for this dangerous blackout”.

Tusk blasts 'absurd' Boris Johnson after Brexiteer's Hitler comments European Council President Donald Tusk today (17 May) launched a scathing attack on Boris Johnson, a leading figure in the campaign to take the UK out of the EU, after the former London mayor compared the EU to Adolf Hitler.

On 17 May, after Tusk’s comments, Commission Chief Spokesman Margaritis Schinas said, “We have refrained from any comments, regardless of their taste, on any comments proffered on the UK referendum and we will not change our position today.”

He later claimed that Hill’s London speech was consistent with that policy.

Schinas said, “The Commission is not party to the campaign – we haven’t been and we won’t be. However it may be the case that Commissioners in the context of their duties will have dealings with the UK and it’s I think perfectly compatible with our basic position.

“In the context of that trip it’s a different matter, it’s not direct participation in the referendum campaign.”

Juncker has also warned that “deserters” from the EU could not be expected to be treated with kid gloves – another apparent departure from the no comment rule.

‘Deserters’ won’t be welcomed back with open arms, Juncker warns Britain “Deserters” from the European Union will not be welcomed back with open arms, European Commission chief Jean-Claude Juncker has warned as Britain prepares to vote in a referendum on whether to stay in the bloc.

Quizzed on that, Schinas said, “Jean-Claude Juncker, after 30 years in public life has earned the right to speak on stakes. But this was not an intervention; this was a reply to your colleagues at Le Monde.”

After publication of this article, Commission spokesman Alexander Winterstein said that Selmayr’s tweet was not a signal the executive preferred Hillary Clinton to Donald Trump.

“I don’t even know if I have to answer that question. The Commission does not express any opinions, either on elections, or electoral campaigns,” he said.

Asked why the Commission had attacked Johnson, Le Pen and Trump, Winterstein said, “You know what the opinion of the President is on populism. He thinks often these people ask good questions, but rarely do they provide practical solutions.

“He generally thinks that that if they think all our problems will disappear if we focus solely on national concerns – that might appear to be a very comfortable approach, but it’s not going to lead anywhere. No country has the clout, either politically or economically, to confront the global threats we face alone.

“As far as the global challenges are concerned, the solutions are to be found together.”

"The Commission does not express any opinions on elections," says Juncker's spox re @MartinSelmayr's attack on BoJo Trump and Le Pen — Matthew Holehouse (@mattholehouse) May 26, 2016

Former UK Prime Minister Gordon Brown also took aim at Johnson during a speech in the European Parliament yesterday.

Gordon Brown calls for EU migration cash to sway undecided Brexit voters Former UK Prime Minister Gordon Brown today (25 May) called for European cash for towns and cities struggling to cope with the refugee crisis, in a bid to convince 14 million undecided Brexit referendum voters to back staying in the EU.