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.

It shows officials having completely lost confidence in the UK’s ability to negotiate, with frustration regularly boiling over at behavior 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.

Guy Verhofstadt, the European Parliament’s Brexit coordinator, 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 Theresa May could not clear it with DUP leader Arlene Foster.

“What the f*** 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 very diplomatic public approach to talks, throughout which they heaped praise on their counterparts such as Theresa May and David Davis.

On another occasion captured in the documentary, Edel Rettman Crosse, 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 the Brexit Secretary did not “really give a f***” about the Irish border, one of the key issues in Brexit talks that bogged down talks for months afterwards.

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

Theresa May’s conference speech also goes down poorly with the team, with Mr McLaughlin shouting “Oh, f*** off!” at the screen when the PM 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.