Plans to cover for striking junior doctors could be put in “jeopardy” if just one or two senior medics go off sick, NHS leaders have warned as the longest walkout in NHS history started.

Hospital bosses said the strike will be “incredibly tough” for the health service as junior doctors in England launched a six-day walkout.

One leader expressed frustration that the British Medical Association (BMA) and the Government have not been able to reach an agreement for “months and months”.

Nick Hulme, chief executive of East Suffolk and North Essex NHS Foundation Trust, said “patients are paying the price” as the dispute rumbles on.

But doctors insisted they are “not hellbent on strikes” and they hoped the Government would resume talks swiftly.

The industrial action, from 7am on Wednesday January 3 to 7am on Tuesday January 9, comes at one of the busiest times of the year for the NHS as it grapples with increased pressure from winter viruses and a rise in people coming forward who delayed seeking help over the holidays.

The NHS has warned that the strike, which could see up to half of the medical workforce in England walk out, could lead to “the most difficult start to the year the NHS has ever faced”.

It said emergency and urgent care will be prioritised during the strikes and almost all routine care will be affected.

Patients are being urged to still come forward to seek care if they need it.

The rotas are just about covered, so it only takes a consultant or two to go off sick... then that is going to put the entire plan in jeopardy

Age UK warned that the threat of strikes could deter elderly people from seeking care.

The charity also said it will be “difficult to guarantee safe and effective care for everyone who needs it”.

Dr Layla McCay, director of policy at the NHS Confederation, told LBC Radio: “In order to maintain patient safety as much as possible, get people the care they need as quickly as possible, all the resources available will be concentrated in the most urgent and emergency care. And that means that that lots of other care will need to be postponed.

“Plans have been put in place and people have been working very, very hard on these rotas. But the rotas are just about covered, so it only takes a consultant or two to go off sick – which, of course, there’s a lot of Covid and flu, norovirus, other winter viruses around at the moment and a couple may go off sick – then that is going to put the entire plan in jeopardy, which is why the leaders across the NHS are so concerned that this is skating on thin ice.”

Sir Julian Hartley, chief executive of NHS Providers, said the strike will be “incredibly tough” for the NHS.

He told BBC Breakfast the NHS is already “under enormous pressure”, adding: “So we are deeply concerned about the kind of impact over the coming days.”

Dr Vivek Trivedi, co-chairman of the BMA’s Junior Doctors Committee, told the PA news agency: “The notion that we’re hellbent on calling strikes and all we want to do is call strikes is not what we want. What we want is to negotiate an offer we can put to our members and for our members to accept it.

“I hope they (the Government) come back to the table now – but from all of the signals they are sending it won’t be until our strike action finishes. And I hope at that point we can come to a resolution.

“So as soon as our strike action finishes we will be asking the Government to get back round the table, which, as we’ve seen from what they have been saying so far, they should be very willing to do very rapidly.

“If the Government stall, or they don’t come to the table, or they make excuses, or they try to push things down the line without any clear reason as to why that is happening… then we will be led by our members.

“In the past when those kinds of actions have been displayed by the Government, our members have wanted us to call for further strike action. I hope that we don’t have to go there but I can’t rule it out.”

My frustration over the months and months now of industrial action has been the inability, or the perceived inability, for the Government and the BMA to get around the table and to compromise and to find a solution

Dr Trivedi said patient safety was maintained during previous strikes and the union would respond to any requests for staff to return to work on safety grounds, known as derogation requests.

Health and Social Care Secretary Victoria Atkins said: “January is typically the busiest time of the year for the NHS and these strikes will have a serious impact on patients across the country.

“I urge the BMA Junior Doctors Committee to call off their strikes and come back to the negotiating table so we can find a fair and reasonable solution to end the strikes once and for all.”

She told Sky News: “We’re very concerned about the consequences it (the strike) will have, not just for this week of industrial action for six days, but also the consequences in the weeks following because of course consultants and other clinicians who are picking up the slack as junior doctors and doctors in training are not at their work, that will be reflected in the weeks coming up with people trying to catch up with the lost time.

“So it’s going to have a huge impact on our health system and my ask of the junior doctors committee is to call off these strikes and get back around the negotiating table.”

But Mr Hulme told LBC Radio: “My frustration over the months and months now of industrial action has been the inability, or the perceived inability, for the Government and the BMA to get around the table and to compromise and to find a solution.

“If you just read the rhetoric that comes from both sides, it seems that there’s an intransigent position, and whilst that continues it’s the patients who are paying the price.

He said that the strikes had “decimated our our plans to attack the long waiting times”, adding that for each cancelled appointment “there’s a life, there’s a delay, there’s not being able to get back to work, there’s an impact on them psychologically, socially and physically, so we need to find a solution quickly.”

Of the 1,219,422 acute inpatient and outpatient appointment cancellations since the current period of strikes began, just over three-quarters (77%) have been on days where junior doctors have taken industrial action either by themselves or with other groups.

The BMA said junior doctors’ pay has been cut by more than a quarter since 2008.

Last summer, the Government gave junior doctors in England an average rise of 8.8%, but medics said the increase was not enough and ramped up strike efforts.

Late last year the Government and junior doctors entered talks, but after five weeks of negotiations the negotiations broke down and more strikes were called.

Junior doctors from the Hospital Consultants and Specialists Association union will join colleagues on picket lines.

Consultants and specialty and associate specialist (SAS) doctors have agreed a deal with the Government, which is being put to members.