Ken Clarke has delivered a sharp warning to both Theresa May and Boris Johnson not make “reckless” spending commitments and destroy the Conservative Party’s reputation for “economic competence”.

Chancellor Phillip Hammond reportedly considered resigning over May’s plans to spend billions of pounds in the dying days of her premiership in order to shore up her legacy.

Boris Johnson, the frontrunner to succeed May, has also floated the idea of cutting taxes for those earning more than £55,000. Although he downgraded this from a promise to an “ambition” during last night’s BBC TV debate.

Speaking during PMQs on Wednesday, Clarke said: “The Conservative Party has frequently won the trust of the public over recent generations because of its reputation for economic competence and responsibility.

“Those qualities have helped to contribute to the prime minister’s legacy which she will leave behind a recovery from economic crisis to full employment and economic growth.”

The former Tory chancellor added: “Does the prime minister agree with me in present uncertainty surrounding Brexit and the change of government it would be extremely unwise for candidates in leadership election for outgoing government to start making reckless commitments to tax cuts and spending promises which should properly be addressed responsibly in a spending round once the uncertainties are behind.”

May said she would “not make any reckless commitments” on her way out the door but wanted to “ensure we see our public services supported”.

Clarke is backing Rory Stewart in the Tory leadership race. During last night’s debate the international development secretary said promising tax cuts at the moment would be “wrong”.

Stewart is seen to be in a battle with Sajid Javid to avoid being eliminated from the race today when Tory MPs hold the third ballot of the contest.

Whoever finishes in last place out of Johnson, Jeremy Hunt, Michael Gove, Sajid Javid, and Stewart will be kicked out of the race.