Strikes by junior doctors in England are going to put the NHS “on the back foot” as it enters its most challenging time of year, the service’s top doctor has said.

Professor Sir Stephen Powis said that the walkouts – set to begin at 7am on Wednesday morning – will cause “huge disruption”.

The industrial action comes as the NHS is already seeing pressure from winter viruses, Sir Stephen warned.

Junior doctors from the British Medical Association (BMA) are to take to picket lines from 7am on December 20 to 7am on December 23 in a major escalation in the bitter dispute over pay.

Doctors in training are also planning to stage the longest strike in NHS history in January – for six whole days starting on January 3.

The NHS has said emergency and urgent care will be prioritised during the strikes and that “almost all” routine care will be affected.

Speaking ahead of the walkout on Wednesday, Sir Stephen, national medical director for the NHS in England, said: “These strikes come at a time that will cause huge disruption to the NHS, with services already feeling the strain of winter pressure.

“When you factor in the Christmas and New Year break, these strikes will prolong that period of reduced activity and it also puts the health service on the back foot into the new year, which is a time where we see demand start to rise significantly.

“Over the holiday period, I would encourage anyone who needs medical help to continue to come forward – in a life-threatening emergency call 999 and use A&E in the usual way. For everything else, use 111 online.”

It comes after the Government and BMA reached a deal over pay reforms for specialist, associate specialist and speciality (SAS) doctors after weeks of negotiations.

As part of the deal, which will be put to members, pay scales will changed, with uplifts of between 6.10% and 9.22% for staff on 2021 contracts.

This is in addition to the increase provided to staff as part of the 2023/24 pay review process.

The Department of Health and Social Care (DHSC) has also committed to a £5 million funding pot to help NHS employers create more specialist roles.

Consultants are currently voting on whether or not to accept a deal struck by the BMA consultants’ committee and the government earlier this month.