First the man behind the plan for a huge multibillion-pound airport hub in the Thames Estuary was skewered in the Tory leadership bloodbath, now the winner herself says she is against the idea.

Theresa May, who will become Prime Minister tomorrow, has told a Medway MP that she is against the so-called "Boris Island" proposal, despite an apparent impasse and drift over the issue of runway expansion in the south east.

As MP for the Berkshire seat of Maidenhead, she has been a stern opponent of another runway at Heathrow, although the issue is already being tipped as being high in her in-tray once she moves into No 10. The Davies Commission has recommended another runway at Heathrow.

Gillingham and Rainham MP Rehman Chishti revealed Mrs May confirmed she did not support the concept of an airport on the Isle of Grain developed by renowned architest Lord Foster. It had been a crucial factor in winning his support, said Mr Chishti.

He hoped that Mrs May’s assurances would bring an end to “the bizarre idea” of Boris Island. “Theresa said it’s not my idea,” said he said. “From the discussion we had she doesn’t support Boris Island."

Mr Chishti was seen standing alongside Mrs May with other supporters when she made her victory speech outside Parliament on a tumultuous day in Westminster on Monday.

Speaking before Andrea Leadsom's decision to quit, he said: "I had a good meeting with her [Mrs May] and she’s someone who provides strong leadership and brings everyone together.

“She’s done a brilliant job as the longest-serving home secretary in the last 100 years. For me, she provides strong leadership and gave me clarity on a local issue.”

Boris Johnson's decision to quit the race last month was welcomed by anti-airport campaigners in Medway - however, Medway Council still has £15,000 in its budget for a campaign against any possible future airport proposals.

Council leader Alan Jarrett has said: “We have kept a watching brief on it. As and when we need to be, we will be ready to lobby again.”