Ed Balls today returned to frontline politics by sharing a platform with George Osborne and Sir Vince Cable to make the economic case for staying in the EU – and used the opportunity to criticise “irresponsible” Boris Johnson.

Former shadow Chancellor Balls made a surprise appearance this morning with Osborne and Cable, who were their parties’ respective economic spokesmen going into last year’s election, in which Balls and Cable lost their seats.

But the joint press conference did not mean that Balls held back when attacking prominent Conservatives, and attacked leading Outer Boris Johnson for a series of outlandish outbursts, including yesterday’s comparison of the EU to the aims of Hitler.

“We’re putting forward solid arguments in my view,” said Balls, referring to those supporting a Remain vote in the referendum. “When I listen to Boris Johnson over the last couple of weeks making accusations that the new Mayor of London is an extremist, that the American President is somehow affected in his views by his Kenyan heritage and the thing he said overnight about Hitler, I think it’s clearly attention-seeking.

“He’s trying to distract attention from the big issues. I think, from my point of view, it shows a massive lack of judgment, and this in the end is about whose judgment you trust.”

“It’s such an ill-judged and irresponsible lack of judgment from Boris Johnson,” Balls added.

Asked why he and Cable had chosen to make today’s intervention with Osborne, one of the architects of their downfalls, Balls said voters always make decisions based on risk, and will do that again in June 23’s referendum:

“I think people understand risk and they won’t want to take a risk with their family finances.

“From my point of view, and Vince’s point of view, they made a different judgement from the one we would have liked. That’s politics.”