Downing Street has denied fresh claims that Boris Johnson and his wife intervened to ensure the evacuation of a Kabul animal sanctuary founder and hundreds of cats and dogs.

Paul “Pen” Farthing, a former Royal Marine, returned to Britain on a chartered plane carrying about 200 dogs and cats at the weekend.

On Monday one of his allies, the animal rights campaigner Dominic Dyer, suggested Carrie Johnson had influenced her husband and encouraged him to speak to Ben Wallace, the defence secretary, before Farthing was given the green light to leave Afghanistan.

“Ben Wallace did it because he was forced to do it when the prime minister came back [from a G7 summit last week] and I have no doubt that Carrie was in on this as well, saying this was turning into a disaster,” Dyer said. He said he had “fed” information to Carrie Johnson, a staunch animal rights advocate.

“I didn’t ask her to contact me, I just said if you can do something or raise concerns. Others were doing the same from different sources,” added Dyer. He claimed Wallace later performed a “U-turn” – with the minister tweeting at 1.33am on Wednesday about granting authorisation for the flight - after being “dragged in” by the prime minister.

A Downing Street spokesperson strongly denied Dyer’s account, saying: “This claim is untrue. This was an operational decision. Neither the PM nor Mrs Johnson were involved.”

The Ministry of Defence declined to comment but sources rejected claims that Farthing’s flight had been delayed or blocked. Farthing was said to have been told that security and access to the airport were the issues rather than a booking slot.

Wallace said on Twitter last week: “Let’s get some facts out there: 1. No one, at any stage has blocked a flight. This is a total myth and is being peddled around as if that is why the pet evacuation hasn’t taken place. 2. I never said I would not facilitate. I said no one would get to queue jump.”

Farthing has meanwhile admitted his emotions “got the better” of him when leaving an expletive-laden message for Wallace’s adviser, Peter Quentin. A recording, obtained by the Times, captured Farthing berating Quentin earlier in the week, accusing him of “blocking” efforts to arrange the flight.

Farthing said he was still trying to ensure the safe evacuation of 68 Afghan animal shelter workers and their relatives, including elderly people and children, who have been cleared to come to Britain.

He said his animal shelter staff had told him to leave without them after attempts to enter the airport were rebuffed by Taliban fighters and after the US had “changed the rules” on entry to the airport.