The shock defection of a Tory MP to Labour in anger over the NHS crisis has heaped pressure on Rishi Sunak ahead of what is already expected to be a tough week for the Prime Minister.

Dr Dan Poulter, a former health minister and working medic, on Saturday quit the Tory Party saying it is “failing” the health service and that he could no longer “look my NHS colleagues in the eye” as a Conservative.

He will take the Labour whip until the general election but will not be running again as the MP for Central Suffolk and North Ipswich, he wrote in the Observer.

Dr Poulter’s move is likely to spook already restive Tory MPs and fuel doubts over Mr Sunak’s premiership.

There is already speculation that a disastrous set of local elections results for the Tories in a few days’ time could galvanise unhappy backbenchers into moving against him.

Mr Sunak has insisted that he intends to call a general election in the second half of the year, but the fallout from the local elections could force his hand, either by leading to a challenge to his leadership or by persuading him that an earlier polling day could be a better solution than limping on with a divided party.

Dr Poulter urged Mr Sunak to call a general election “as soon as possible” as he ditched the governing party.

Dr Poulter told the newspaper the Conservative Party “feels like it has become a nationalist party of the right”.

“The health service has ceased to be an area of priority for the Conservative Party, and that is now showing in the strain on the front line and the deterioration of care for patients,” he said.

He added that he had come to the conclusion that “the only cure is a Labour government”, and he would support Sir Keir Starmer and shadow health secretary Wes Streeting on NHS policy.

The Conservative Party hit back that he was “wrong” to say only the Opposition could improve the health service.

Speaking to the BBC’s Laura Kuenssberg, Dr Poulter said: “I found it increasingly difficult to look my NHS colleagues in the eye and my patients in the eye and my constituents in the eye with good conscience.

“And I feel that the NHS deserves better than it has at the moment in terms of how it’s run and governed.”

He added that the Tory Party’s “focus is not on delivering or supporting high-quality public services”.

Labour leader Sir Keir said it was “fantastic to welcome Dr Dan Poulter to today’s changed Labour Party” and that it was “time to end the Conservative chaos”.

Mr Streeting said he looked forward to working with the frontline clinician, especially on mental health reform.

It is the first time a Conservative MP has crossed the floor to Labour since Christian Wakeford did so in 2022.

Dr Poulter’s move is the second defection under Mr Sunak, after former Tory deputy chairman Lee Anderson left the party for Reform earlier this year.

The Telegraph reported that a group of Tory rebels have devised a plan to oust the Prime Minister and unite around Commons Leader Penny Mordaunt, though a source close to the Cabinet minister said “it’s total hogwash”.

“We’ve heard these rumours time and time again. Always lacking substance. Idle speculation is not helpful to anybody but those wishing to cause chaos,” the source said.

Dr Poulter was first elected to Parliament in 2010. He held his Central Suffolk and North Ipswich seat at the 2019 election with a majority of 23,391.

A Tory Party spokesperson said: “For the people of Central Suffolk and North Ipswich this will be disappointing news. What Dan says is wrong as Sir Keir Starmer has no plan for our NHS.

“Under the Conservatives we are raising NHS funding to a record £165 billion a year, helping it recover from the effects of the pandemic and driving forward its first ever long-term workforce plan so that we train the doctors and nurses we need for the future in our country.”