Tory MPs have criticised Theresa May’s “disappointing” response to a cross-party demand that the government move urgently to deal with the future of NHS and social care.

Sarah Wollaston, the chair of the Commons health committee said the prime minister had showed she “lacks ambition”.

Johnny Mercer, the Plymouth MP and former soldier who campaigns on mental health issues, suggested the government was heading for an election defeat with a “reality check at the ballot box”.

It comes as a YouGov poll suggested 73% of Tory voters believed the state of the was a NHS serious concern.

In November, 90 MPs, including 33 Conservatives, signed a letter calling for a NHS and Care Convention to be set up to come up with a “sustainable” system for healthcare.

The prime minister responded with a three paragraph letter on Sunday evening.

Theresa May’s response to cross-party NHS letter

In their letter to the prime minister, the MPs said: “The need for action is greater now than ever.

“We understand that fixing this is immensely challenging and involves difficult choices.

“We all recognise, though, that patients and those needing care are too often failed by a system under considerable strain. We believe that together we owe a duty of care to the people of this country to confront the serious challenges to the NHS and the social care system.”

May’s response did not go down well with many of the Tory MPs who had signed the initial letter.

MPs from other parties also sharply criticised May including former Lib Dem coalition health minister Norman Lamb and Liz Kendall, the former Labour shadow minister for care and older people.

Grant Shapps, the former Tory party chairman, last night told the BBC’s Westminster Hour that “nothing” had changed his view since the party conference in October that May should resign.

Boles, who criticised May’s NHS response, also warned on Friday: “There is a timidity and lack of ambition about Mrs May’s Government which means it constantly disappoints. Time to raise your game, Prime Minister.”

The Tory frustration with May comes amid severe winter pressures on the NHS that have seen thousands of operations delayed.

The prime minister has insisted that the health service was “better prepared” than ever before this year.

In her Cabinet reshuffle, May agreed to Jeremy Hunt’s plea to keep in him in place as health secretary and expand his title to include social care.