A leading surgeon has raised concerns that cancer operations could be cancelled if the NHS becomes overwhelmed with Covid-19 patients.

The health service has done its best to maintain cancer operations and other emergency services throughout the pandemic, but with new cases at a record high, the surgeon has raised concerns over the possibility of cancer operations being cancelled or postponed.

Medical staff in London in particular have been reporting problems with staff numbers on wards and in theatres, and the capital now contains nearly half of the top 20 areas with the highest infection rates in the country.

And potentially life-saving cancer operations have already been put on hold at the King's College Hospital Trust because of the number of hospital beds taken up by Covid patients.

Professor Neil Mortensen, president of the Royal College of Surgeons, said that many places had already stopped lower priority surgeries such as hip and knee replacements.

He told Times Radio: "Over the weekend we talked about a slow-motion car crash, but I think it's getting much worse than that now.

"My colleagues in London doing ward rounds, for example, report that there are problems with staff numbers on the wards, staff numbers in theatres.

"And then of course if you need to go to the intensive care unit, if the intensive care unit is full of Covid patients, there's no room for you.

"So it's a really serious situation and, obviously, the less-priority operations have already stopped in many places - hips, knees, ENT (ear nose and throat) procedures.

"We're now concerned about operations like cancer surgeries being cancelled or postponed because there just isn't the capacity to be able to manage them."

Prof Mortensen added: "I think if you have a delayed operation for cancer that may have an effect.

"If you come in from a road traffic accident and you're seriously ill, and you need to go to an intensive care unit afterwards and there is no intensive care unit, that's going to have serious consequences.

"And that's why everybody is so concerned right now that we are properly locked down, that we're as far as we possibly can reducing the transmission of the virus, and making it possible for what facilities we do have to carry on working effectively to keep people alive."

Prof Mortensen said that there will not be capacity in hospitals to treat other illnesses without reducing transmission of the virus.

"There needs to be space in our hospitals for us to deal with all the other things - the heart attacks or strokes, the cancer surgeries and emergency surgery," he added.

"We have to be able to keep capacity to do those. And if we don't reduce the transmission of the virus, there won't be that capacity."

When asked whether the NHS will be able to return to normal business by late spring, he added: "I'm afraid I'm one of the pessimists I think this is going to drag on a bit.

"I think that we're really not going to be any bit in any better shape (until) summer, I'm afraid.

"I think it's going to take a long time. This is a very, very, very serious situation.

"There'll be an enormous backlog of elective surgeries, and we may have backlogs of some more urgent surgeries to get through as well so it's going to be a long, tough, hard winter and spring."

Sara Bainbridge, head of policy at Macmillan Cancer Support, said: "We still must make sure that cancer doesn't become 'the forgotten C' during this time and it is imperative that people expecting tests and treatment face minimal disruption.

"However, if disruption is unavoidable to keep people safe, then cancer patients expecting to undergo surgery this week will be understandably concerned.

"This decision would represent one of the toughest choices that clinicians will ever make and is a grim indication of how overwhelmed many hospitals are becoming with Covid admissions.

"It's vital that all decisions are based on patients' individual circumstances and are communicated directly by clinical teams.

"Cancer patients need to be reassured that everything possible is being done to ensure that they will receive the necessary treatment as soon as possible, and know who to contact if they have questions.

"For those who need it, our free helpline (0808 808 00 00) is available seven days a week, providing clinical, practical and financial support."

Kruti Shrotri, Cancer Research UK's head of policy, added: "It's extremely concerning to hear that cancer surgery is being delayed in some parts of the country, and this shows just how much the NHS is struggling to cope.

"We know NHS staff are doing everything they can to protect services and deliver urgent cancer care.

"During the first wave, the independent sector enabled some cancer surgery to continue so it's vital that this option remains available for NHS use.

"Ultimately, lowering Covid cases is the answer to take the pressure off the NHS which is where we can all play our part.

"To those who are experiencing delays and cancellations, we understand how incredibly hard this is, and we're doing all we can to support the NHS to protect cancer services.

"Anyone who thinks they might have signs or symptoms of cancer, please go and see your GP - the NHS is still open to see you."

A spokesman for the NHS in England said: "NHS trusts continue to treat as many elective patients as possible, and prioritising those who have been waiting the longest, whilst maintaining cancer and urgent treatments.

"However, the health service is under severe pressure and urges the public to follow Government social distancing guidance."

Concerns were raised after the Prime Minister warned that hospitals are under more pressure from Covid-19 than they have ever been.

Announcing the new lockdown in England on Tuesday, Boris Johnson said that hospitals are 40% busier than the first peak of the virus in April 2020.

Almost 27,000 people are being treated in hospitals across England.

It comes after the UK's chief medical officers raised the Covid-19 alert level to five - its highest - meaning "transmission is high or rising exponentially" and "there is a material risk of healthcare services being overwhelmed".

The alert level has not been at level five before.

It indicates a risk of healthcare services being overwhelmed within 21 days without urgent action - it does not mean the NHS will be overwhelmed in three weeks, but there is a risk of that happening if no action was taken.