Thousands of people a month are getting private treatment that is paid for by the NHS, the BBC has learnt.
Since 2006, patients have been allowed to choose where they receive treatment, whether in an NHS hospital or a private healthcare unit.
A BBC report reveals that the number of people opting to stay in private hospitals has risen tenfold to over 3,500 a month in just over 12 months.
These patients benefit from the facilities available to those who pay for private treatment, including private rooms, free parking and a lower rate of hospital infections such as MRSA.
As a result, the NHS reportedly spends £7.6 million in fees to private hospitals such as Ramsay Healthcare centres.
A spokesman for the Department of Health told the BBC: "Choice gives providers the incentive to tailor services to the needs and preferences of patients which, in turn, will lead to better outcomes and the reduction of health inequalities."
A number of NHS Trust hospitals also have private units, including Hammersmith Hospitals NHS Trust and the Oxford Radcliffe Hospitals.
Who can you complain to about private hospital care?