Hospitals are having to cancel operations and cancer scans are going unread for weeks because consultant doctors have suddenly begun working to rule in a standoff over NHS pensions.

Doctors say the dispute is escalating so quickly that it will send NHS services “into meltdown” and is so serious that it poses “an existential threat” to the health service’s survival.

Changes to pension rules in 2016 mean rising numbers of consultants are receiving large bills linked to the value of their pension. Some are having to remortgage their homes to pay.

Waiting times for treatment, already the worst on record, are worsening as hospitals struggle to find senior doctors prepared to work more than their planned shifts, which could lead to them receiving a pension tax bill of as much as £80,000.

NHS bosses fear the total number of patients in England waiting for non-urgent care such as a hip replacement or hernia repair, which already stands at 4.4 million, could soon head towards 5 million.

The Royal Bournemouth hospital in Dorset may have to cancel scores of operations between now and 27 July because none of its consultant anaesthetists are prepared to help staff the 53 sessions of surgery, involving up to 150 procedures, that are currently uncovered because no one from that speciality has signed up to attend.

The situation has arisen because its anaesthetists fear that by working over and above their usual hours they will end up financially worse off.

At another hospital the number of patients who have been waiting more than the 18-week supposed maximum for a planned operation has risen from 3,000 to 4,500 since April for the same reason.

“The pensions catastrophe is an existential threat to our NHS. We’re only just beginning to see the impact of these taxes. As more doctors get affected, it’s going to get a lot worse,” said Dr Tony Goldstone, a consultant radiologist and clinical director at Hull University teaching hospitals NHS trust, who is also an expert on NHS pensions.

“As a frontline clinician and clinical director, the stark reality of the pensions taxation is now becoming abundantly clear. Not only in my own trust but up and down the country there are reports of backlogs of unreported cancer scans – higher than they have been for years.

“Colleagues who used to help prop up services by working additional weekends, on top of their already onerous working rotas, can no longer afford to do this. I am hearing of operating theatres not being utilised because of the inability to staff them, and rota gaps not being filled as senior staff are unable to help out.”

Consultants’ decisions also mean that hospitals are also struggling to find enough doctors to fully staff shifts in their A&E or acute medical unit. The resulting gaps in rotas pose a potential threat to the quality and safety of care, NHS leaders say.

Full-time doctors are usually contracted to undertake 10 “programmed activities” – four or five-hour shifts – a week, but most consultants do 11 or 12. That extra work helps the NHS’s effort to keep up with the fast-rising demand for care. However, more and more consultants are dropping sessions because, by earning less, their pension pot grows more slowly and their risk of being hit with a big bill is reduced.

Chris Hopson, the chief executive of NHS Providers, which represents NHS trusts in England, said hospital bosses were finding it increasingly difficult to provide a normal range of services, especially “catch-up” sessions of surgery to tackle waiting-list backlogs.

In the last month there has been a sharp increase in consultants pulling back from the extra work because they believe that the government’s proposed solution – contained in the interim NHS People plan for England, published on 3 June – will not work.

The so-called 50/50 scheme would let senior doctors put less into their pension for up to 10 years to reduce the risk of their pot hitting the £1.1m maximum.

Hopson said: “Staff are voting with their feet. Trust leaders report that over the last month they have had significant numbers of key clinical and managerial staff saying they can no longer afford to work extra shifts and weekends because of the financial penalties involved in doing so, due to the way that the pension taxation rules currently work.

“To quote two examples we’ve heard just this week, a senior anaesthetist who worked 27 Saturdays last year to reduce waiting lists has now said he cannot afford to work any extra Saturday shifts this year because it would give him a large tax bill he cannot afford to pay.

“Another trust’s medical director, a senior A&E consultant who routinely worked most Sundays last year and was key to providing safe emergency care for that trust, is now unable to work any Sunday for similar reasons. In both cases, the trust’s performance [on waiting times] and the quality of patient care risks being compromised.”

A row over working hours, again triggered by huge pension tax bills, is brewing at University College London hospitals trust, one of the NHS’s biggest and best trusts, which has also had to cancel planned extra sessions of surgery.

In a letter to its consultants last week, Ben Morrin, the trust’s workforce director, made clear to them that despite their growing reluctance to work beyond their usual hours, “the expectation remains that consultants, including part-time and clinical academics, should offer up to one extra programmed activity per week on top of the standard commitment set out in his or her contract of employment before undertaking private practice to the trust”. Consultants plan to respond “robustly”.

A consultant at one trust said that unless ministers acted, about 30% of total consultant time could become unavailable to the NHS, if enough kept scaling back their hours. “This also has an effect on emergency care and out-of-hours rotas, particularly where there are rota gaps, where there is now a tax penalty in filling those gaps with in-house consultants. This is a real risk in providing safe care. A consultant told me only yesterday they had an unexpected bill of £75,000.”

Prof Joe Harrison, the chief executive of Milton Keynes university hospital trust, said: “Although this hasn’t affected us yet in terms of consultants reducing hours, this may well start to change as we near the end of the tax year. If this were to happen – which is just as winter begins in earnest – the impact on our ability to provide safe care, both for patients needing planned operations and procedures and those needing emergency care, would be severely compromised.”