NHS waiting lists have hit a record high of 5.3million patients.
The backlog caused by the pandemic is building while A&E visits soared to 2.16million last month, 50 per cent more than in June last year.
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And NHS Providers, which represents hospitals, said forcing fully vaccinated staff to self-isolate was proving another major headache.
Chief executive Chris Hopson said: “We’re going full-pelt on recovering care backlogs, with many trusts saying they saw record levels of daily demand in June.
“We’ve also got 10 per cent fewer beds in the NHS at the moment because of infection control measures.
“But as community infection rates of Covid rise, we’ve got more and more staff who are having to self-isolate.
“If the river is full and the ground is sodden, all you need is a few extra cases of Covid and that river will start to overflow.”
New NHS data showed the number of people waiting for treatment is the highest it’s ever been since records started.
