EU officials involved with Brexit negotiations privately considered aspects of Theresa May’s approach “insane” and “pathetic”, a new behind-the-scenes documentary shows.

BBC camera crews were given access to Brexit officials in the European parliament to make Brexit: Behind Closed Doors, a two-part series focusing on the team around Guy Verhofstadt, the European parliament’s Brexit coordinator.

It shows officials having completely lost confidence in the UK’s ability to negotiate, with frustration regularly boiling over at behaviour emanating from the government in London.

In one telling scene, chief EU negotiator Michel Barnier, says his team needs someone “stable, available and reliable” on the British side to hold discussions with.

Mr Verhofstadt sarcastically replies: “We can’t ask too much of Britain, don’t overdo it.”

In another scene, Mr Verhofstadt’s chief of staff Guillaume McLaughlin reacts with disbelief when he is told that a Brexit deal is off because Ms May could not clear it with DUP leader Arlene Foster.

“What the f**k is wrong with her. That’s insane. ‘I don’t know, I haven’t spoken to her?’ That’s ridiculous. Pathetic, pathetic,” he says.

The comments are in contrast to the EU’s diplomatic public approach to talks, throughout which they heaped praise on their counterparts such as Ms May and David Davis.

On another occasion captured in the documentary, Edel Rettman-Crosse, Mr Verhofstadt’s top aide, describes the UK’s then Brexit secretary Mr Davis, who the team has just met with, as having his “head in the f***ing clouds”.

The officials agreed that Mr Davis did not “really give a f**k” about the Irish border, one of the key issues that bogged down Brexit talks for months afterwards.

Mr Verhofstadt represents the European parliament in Brexit talks (AP)

“David Davis explained to us that Ireland is not a problem,” says an exasperated Mr McLaughlin, recounting the meeting. The Brexit deal has since been blocked by the UK parliament effectively over the Irish border question.

Ms May’s conference speech also goes down poorly with the team, with Mr McLaughlin shouting “Oh, f**k off!” at the screen when the prime minister claims she is working hard to get a deal.

The film also gives the impression of a Brussels that feels totally unthreatened by the UK, with regular mocking doled out at the UK’s expense.

Over breakfast in one scene, Mr Verhofstadt and Mr Barnier end up discussing classic cars, and Mr Barnier jokes: “That’s what they’re trying to do with Brexit, take an old car and restore it.

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Elmar Brok, a German ally of Angela Merkel who sits on the Brexit steering group, says the EU should not help the UK sort out its “mess”.

“I am very clear we have to do nothing. We are ready and they have to come,” he advises. “And we have to wait while the air becomes thinner and thinner because we lose time.”

On another occasion, officials are also bemused at Ms May’s invocation of “war spirit” in her conference speech.

After one encounter in which Mr Verhofstadt has an argument with Brexiteer Tory MP Andrew Rosindell, top aide Ms Rettman-Crosse tells her boss: “I’m most proud of you when you take on a Tory. He was a f***er.”