A top EU official has accused the UK’s Brexit negotiators of “running around like idiots”, comparing UK ministers to the hapless characters from classic TV sitcom Dad’s Army.

Frans Timmermans, the European Commission’s vice president, said leaders in Brussels believed British ministers would produce “Harry Potter-like” trickery when they began negotiations in 2017.

Instead they acted like Lance Corporal Jones from the classic sitcom, Mr Timmermans told BBC’s Panorama programme, set for broadcast on Thursday night.

“We thought they are so brilliant that in some vault somewhere in Westminster there will be a Harry Potter-like book with all the tricks and all the things in it to do,” he said. “Then the first time I saw public utterances by David Davis ... I thought: ‘Oh my God they haven’t got a plan’.

“That was really shocking frankly because the damage if you don't have a plan … it’s like Lance Corporal Jones you know, ‘Don’t panic, don’t panic’, running around like idiots.”

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Mr Timmermans also accused Boris Johnson of “playing games” with Brussels when he was foreign secretary. He was not sure Mr Johnson was ever “being genuine” in his approach to the EU and Brexit.

“Perhaps I am being a bit harsh, but it’s about time we became a bit harsh,” the European Commission official added.

Also interviewed for the BBC programme, the EU’s chief Brexit negotiator Michel Barnier said the UK “will have to face the consequences” if it crashes out of the union without a deal.

Mr Barnier also said the outgoing prime minister Theresa May and her ministers “never” suggested they might opt for a no-deal Brexit during negotiations.

He said: “I think that the UK side, which is well informed and competent and knows the way we work on the EU side, knew from the very beginning that we’ve never been impressed by such a threat. It’s not useful to use it.”

However, Ms May's official spokesman later insisted: "The Prime Minister was clear in her discussions in public or in private that the UK could leave without a deal."

The European Commission’s top official Martin Selmayr, meanwhile, said he thought the UK was still unprepared to leave without a deal.

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“We have seen what has been prepared on our side of the border for a hard Brexit. We don’t see the same level of preparation on the other side of the border.”

The EU secretly offered to put Brexit “on ice” for five years in order to come up with a new deal for Europe, Ms May’s de facto deputy David Lidington told Panorama.