Passionate Brexiteers are seen as a “bunch of emotional nutcases” outside of the UK, former Tory Treasury minister Lord O’Neill has said. 

The ex-Goldman Sachs chief economist, who quit his post as a minister last autumn, also hit out at Leave backers “trashing” civil servants in the Treasury, calling their claims “ridiculous nonsense”. 

Tory MP and hardline Brexiteer Jacob Rees-Mogg said this week he believed there was an “orchestration” of pro-Remain stories and he is “suspicious” of the Treasury’s economic models in the wake of leaked analysis. 

But ignoring evidence and attacking civil servants led other countries to view Brexiteers as “emotional nutcases,” said O’Neill. 

The George Osborne-ally also told BBC Radio 4′s World At One programme Leavers had to be “realistic” about how EU withdrawal could hit the economy, as he voiced fears about sectors such as the car industry in particular.

He said: “Without the single market and access to this highly integrated global supply chain, that industry and many of them like it are going to have serious challenges being anything like as good as they are today.

“There may be other reasons why passionate Brexiteers choose to ignore, or trash those things – and this ridiculous nonsense about trashing the civil service – but they need to be realistic.

“And, perhaps, the whole argument might be better if they just acknowledge that those industries are going to have new challenges.

“Because, otherwise, their own arguments just don’t have any credibility whatsoever.

“And, it also adds to other countries, sort of, thinking the UK is full of a bunch of emotional nutcases.”

Lord O’Neill has previously described Foreign Secretary Boris Johnson as “ludicrous”.

It comes after Brexit minister Steve Baker was this week forced to apologise after airing a false claim in the Commons that civil servants were working to undermine Brexit. 

In an extraordinary exchange in the Commons on Thursday, Baker had said it was “essentially correct” that Treasury officials had tried to sabotage Brexit by skewing analyses to suggest the economy would suffer under every scenario other than remaining in the Customs Union.

The Prime Minister rebuked Baker for his remarks, stating he would have to officially say sorry to Parliament in line with the ministerial code requiring an early correction.