James Daley of Fairer Finance, a ­ratings service, said policyholders paid costly premiums in order to access medical care and to avoid lengthy NHS queues. “It is therefore reasonable to expect to get your money back when your insurer is not able to provide the services you have paid for, or has provided a substandard alternative such as physiotherapy via a webcam rather than in person,” he said.

A dearth of claims during lockdowns – when private healthcare providers were permitted to offer only urgent cancer treatment as well as some basic services such as online and video conferencing check-ups – allowed insurers to collect vast sums as monthly premiums continued to roll in regardless.

Most said they would return the unearned profits but customers will have to wait years before they get anything back in some cases.

Mr Daley said: “This is a case of insurers looking after themselves and their shareholders rather than their customers. They are dragging their feet on payouts and making excuses, seemingly delaying things until people forget and no one notices any more.

“They cannot keep using the pandemic as an excuse – it could be going on for years. Customers may have died before they see this money back.”

However, so far Bupa is the only firm to live up to its promise: it has returned £125m to customers since it began to make payments in April last year.

Axa said it would begin to issue refunds to policyholders who were ­unable to access treatments from March, although it declined to say how much it would pay out. It said it had received assurances that urgent private medical services would be protected for all patients regardless of whether or not the sector was required to help the NHS.

Aviva, which charges customers more than £1,000 a year on average for access to private care, said it needed more time to audit its records to understand the impact on claims numbers. It said it was monitoring the situation in case private hospitals were called on again by the NHS. It will not be in a position to refund customers until the end of the year at the earliest, it said. A spokesman added that “numerous subsequent lockdowns have meant that it will take longer than initially expected”.

Saga said it was still reviewing its books and would hire an independent third party to audit its claims history to review the overall impact of the pandemic at the end of the financial year.

Vitality has decided against refunding customers altogether and said it “always ensured that our premiums change fairly for members, meaning renewals automatically consider the level of claims we have had in the past year, and therefore over the pandemic”.

A spokesman added: “We will ensure that our members both received and continue to receive value from their products and that they are treated fairly at all times.”

The Association of British Insurers trade body said private medical customers should still come forward for diagnosis and treatment as usual.