A third of NHS contracts in England have been awarded to private firms since the Coalition Government's health reforms came into force last year, according to official figures.
A Freedom of Information request, obtained by the British Medical Journal (BMJ), found that there were 3,494 contracts awarded by 182 Clinical Commissioning Groups (CCGs) in England between April 2013 and August 2014.
An analysis of the data revealed that 33% (1,149 contracts) of those contracts went to the private sector.
The research also found that 55% of the contracts went to the NHS, while 10% went to voluntary and social enterprise providers, 4% were given to other types of provider.
"These figures blow apart Jeremy Hunt's claim that 'NHS privatisation isn't happening'. It is happening and it is happening on his watch," said Andy Burnham, Labour's Shadow Health Secretary.
"This is because contracts are being forced out onto the open market by David Cameron's Health Act.
"Labour believes in protecting the public NHS and will repeal the rules that are fragmenting and privatising it.
"The NHS of the future demands more integration. The problem with this government's policy is that it's taking it in the opposite direction, towards more fragmentation."
But the government claimed that the data is misleading since it does not disclosure how much the contracts were worth.
"Official NHS accounts show that use of the private sector amounts to only six pence in every pound the NHS spends, slowing the rate of increase to just one penny since May 2010," a Department of Health spokesperson said.
"Charities, social enterprises and other providers of healthcare play an important role in the NHS, as they have done for many years."
The investigation also looked into how much the NHS spend on management consultants.
The probe found that the cost of the consultants had rocketed to £640m ($1,003m, €810m), from £313m in 2010, under the Coalition.
Professor David Oliver, a former clinical director at the Department of Health, who uncovered the spending, compared the outside experts to "arms dealers".
"In times of war, arms dealers, rebuilders, and racketeers profit from the chaos," he wrote in the BMJ.