Sir Keir Starmer has threatened to withdraw an offer of thousands more NHS jobs should resident doctors go ahead with strike action next week.
The medics – formerly known as junior doctors – are planning to walk out for six days from 7 April, just after the Easter bank holiday weekend.
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It will be the 15th round of strikes by resident doctors in England since 2023, in an ongoing row over pay and jobs.
Sir Keir has condemned the planned action as "reckless" and given them 48 hours to reconsider.
Writing in The Times, he said the British Medical Association's (BMA) resident doctors' committee had rejected a "historic deal" that would have delivered "another above-inflation pay rise this year" of 3.5%.
It would bring the total pay rise over three years to 35%, the prime minister added.
'Wrong decision'
He said the government's proposal would also have delivered reforms to pay progression to reward doctors as they gained experience and responsibility, reimbursed the cost of Royal College exams, and provided up to 4,500 extra speciality training places over the next three years.
The measures "are the result of months of collaboration with the BMA, who engaged constructively throughout", the prime minister said.
"That is why walking away from this deal is the wrong decision. It is a reckless decision. And doing so without even giving resident doctors themselves the chance to vote on it makes it even worse," he wrote.
Sir Keir warned each round of strikes costs the NHS £250m paying for cover and would threaten the progress he said Labour had made in improving wait times for patients.
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The BMA's resident doctors' committee has defended rejecting the deal, citing the cost of living and expectations that inflation will rise as a result of the Iran war.
Chairman Jack Fletcher said in a statement last week: "We cannot ignore that, thanks to global events, economic indicators now point to years of greatly increased inflation.
"We are simply not going to put an offer to doctors that risks locking in further erosion of pay at a time when doctors continue to leave the UK for other countries."
He insisted the committee was still "willing to negotiate".
The Tories have said the continued threat of strikes despite pay rises already handed out by the government proves "stronger action is needed", namely a ban on doctors' strikes.
(c) Sky News 2026: Starmer issues 48-hour ultimatum over 'reckless' doctors' strikes
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