The Nuffield Trust report warned the rise in private sector provision risked entrenching health inequalities by determining the availability of care based on financial resource rather than need in a context of general scarcity.

Mark Dayan, Nuffield Trust's policy analyst and head of public affairs, said: 'While the vast majority of care remains NHS funded and delivered, there has been a definitive shift in all four UK countries towards private healthcare either funded out of pocket or to a lesser extent through private healthcare plans.'

Analysis of PHIN (Private Healthcare Information Network) data between September 2019 and 2023, showed the number of self-payers tripled in Northern Ireland (up 218% from 800 to 2,560 per quarter), more than doubled in Wales (up 124% from 1,865 to 4,100) and almost doubled in Scotland (up 80% from 2,835 to 5,165).

In England, which continues to have the highest number of privately funded care relative to its population, there was a rise of 20% from 45,000 to 54,000.

The number of admissions and day cases covered by private healthcare insurance has also grown since the pandemic (up 5%), although this growth was largely towards the end of 2023, the report found. Northern Ireland again saw the biggest increase in hospital care covered by private healthcare plans (a rise of 250% during the same period).

Despite record levels of staffing and greater levels of funding within the NHS, the report found trusts in England provided fewer hospital admissions in 2022/23 than before the pandemic.

The research also found substantial growth in spending by NHS trusts in England on private care with spending nearly doubling (an 88% increase) between 2019/20 and 2022/23.

The proportion of patients in private hospitals in England rose from 5.6% before the pandemic to 7.5% in 2022/23. An average of 30,000 more patients a week were treated privately within the NHS in England.

A Department of Health and Social Care spokesperson said: 'We are taking the long-term decisions needed to make our health service in England faster, simpler and fairer, cutting waiting lists and ensuring people get the care they need.

'The overall NHS waiting list which has fallen by around 200,000 over the past six months and we are continuing to make good progress, while delivering record numbers of diagnostic tests, record levels of investment and embracing the latest technology across the NHS to deliver care to people when and where they need it.'