Virgin has been awarded almost £2 billion worth of NHS contracts over the past five years, according to new analysis.
The Guardian reported that the company and its subsidiaries hold at least 400 contracts across the public sector - from healthcare in prisons to school immunisation programmes.
According to the newspaper, NHS services contracted out include: sexual health services in the north-east of England, some GP surgeries in Essex, healthcare in a number of low-category prisons and a contract with NHS England to give school flu jabs in Devon.
Commenting on the analysis, Dr Robert Harwood (pictured), chairman of the British Medical Association's consultants committee, said: "We firmly believe that the NHS should be publicly funded and publicly provided, and that ultimately the introduction of a competitive procurement framework has been, and will continue to be, detrimental to the health service.
"Patient care simply cannot take second place to finances nor damaging legislation. At a time when the NHS is facing huge financial pressure, it is vital that taxpayers' money is used to support overstretched NHS services to provide high-quality, safe care to patients, not to fund multimillion-pound private contracts."
Sara Gorton, the head of health at the trade union Unison, told the newspaper: "The company has been so keen to get a foothold in healthcare, it's even been prepared to go to court to win contracts, moves that have cost the NHS dearly."
Labour's shadow health minister Justin Madders said: "The Tories' expansion of the internal market has led to one third of contracts being awarded to private providers since the Health and Social Care Act. Some of these contracts are vast and their failures have wasted millions of pounds of public money.
"After the biggest funding squeeze in NHS history it is essential that every penny is going to frontline services and to improving patient care, rather than padding out private profits."
Commenting on the story, Theresa May's official spokesman said: "As the Prime Minister has said many times in the chamber, the NHS is not for sale and it never will be.
"As spending on the NHS has increased, private sector spending remains proportionately low and we remain clear that the NHS will remain free at the point of use both now and in the future.
"Any decisions about use of the private sector are taken locally by local doctors who know their patients best."
Union Unite called on MPs on the Health and Social Care Committee to look into private healthcare involvement with the NHS.
Sarah Carpenter, head of health at the union, said: "The Commons health and social care select committee should investigate how Richard Branson's Virgin empire has gobbled up nearly £2bn of NHS contracts in the last five years.
"With the spectre of Carillion still haunting the public sector, the select committee needs to urgently examine whether the NHS and taxpayer is getting value for money from Virgin Care accumulating so many health service contracts.
"The scope of such an inquiry should be widened out to look at private healthcare companies, and the scale and scope of their involvement in the NHS generally, as well as the potential impacts and risks that this may have."
A spokesman for Virgin Care said: "For more than 10 years we have been supporting the NHS and local authorities to deliver health and care services; we have saved the taxpayer millions and delivered the plans asked for by the NHS - 93% of people rating our services say they'd recommend them.
"We have not made a profit to date, investing all money in delivering and improving the services we run and supporting a free, efficient NHS."
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