BORIS Johnson’s controversial trip to Afghanistan while MPs voted on whether to push ahead with a third runway at Heathrow cost taxpayers at least £20,000, it has been revealed.

The former foreign secretary missed the key Commons vote despite his long-term opposition to the expansion, which he once claimed he would lie down in front of bulldozers to prevent.

He was accused of hastily arranging talks in Kabul to avoid collective responsibility as a Cabinet member, which would have forced him to resign if he opposed the Government-backed project.

Investigative website The Ferret asked for the full cost of his trip.

The Foreign and Commonwealth Office (FCO) revealed £19,366 was spent on flights and other expenses for three staff who accompanied Mr Johnson.

But it refused to provide details for Mr Johnson himself, insisting the information would be published “in due course”. It also refused to detail security costs, or to reveal when the trip was first discussed.

Scottish Labour MSP Neil Findlay branded the visit a “misuse of £20,000 of taxpayers’ money” in a bid to save Mr Johnson embarrassment.

He told The Ferret: “It looks like this was another occasion when Mr Johnson disgraced both his former office and the Tory government.”

Mr Johnson’s whereabouts ahead of the crucial vote in June was only revealed when the Afghan government tweeted pictures.

He said he was “proud and inspired” to be in Kabul to see how the UK is supporting efforts towards peace and a political settlement.

He added: “I was hugely impressed by the work done by British troops as part of this Nato mission and I believe there is still a lot the UK could contribute to this vital operation.”

But he was widely condemned for missing the Heathrow vote, which the Government won by 415 votes to 119 – a majority of 296.

Tory MPs faced a strict three-line whip to back the expansion, but Mr Johnson has opposed a third runway for more than a decade.

After being elected MP for Uxbridge and South Ruislip in west London, he told supporters: “I will lie down with you in front of those bulldozers and stop the building, stop the construction of that third runway.”

Despite the row, he resigned as foreign secretary just two weeks later, on July 9, over Prime Minister Theresa May’s Brexit plans.