Health service leaders said this was because permanent hospitals in the capital are so far coping with the flow of Covid-19 patients.
However, the NHS Providers report suggests that, if hospitals had had better pre-existing capacity, fewer non-Covid 19 services would have had to be disrupted to allow for extra critical care beds.
“Compared to many other equivalent first world health systems, the NHS has much less spare capacity, regularly running at 90-95 per cent bed capacity when other systems, like Germany’s run at 80 per cent,” it said.
“This means that if the NHS is to create capacity to treat pandemic victims, it has to discharge medically fit patients and divert planned care.”
Professor Karol Sikora, formerly the chief of the World Health Organisation’s cancer programme, said: “My view is we’ve got to pull all the stops to get cancer and cardiac patients flowing through the system by the end of this month. This needs to be factored into decisions on lockdown, otherwise more people will die.”
In March, health service leaders published guidance telling frontline staff that they may have to ration cancer services to those patients most likely to survive in the event of a surge of Covid-19 patients.
Meanwhile, the National Institute for Health and Care Excellence warned that, for some cancer patients, it may be more dangerous to risk catching coronavirus by coming in to hospital than delaying treatment.
The new report found that the supply of ventilators for coronavirus patients is so far keeping pace with demand, partly because the number of patients requiring mechanical ventilation is lower than originally estimated.
However, trust leaders report that a large number of patients, not necessarily elderly or with long-term conditions, “can quite quickly develop multiple organ failure”.
An NHS spokesman said: “The NHS is pulling out all the stops and staff are working around the clock to respond to the coronavirus pandemic, while at the same time ensuring that essential and urgent cancer diagnosis, treatment and care can continue.
“There is capacity across the country and, if you have a cancer symptom, you should still contact your GP and be referred for further checks as normal so you can continue to access the services you need in as safe a way as possible.”