Spending on private ambulances by the National Health Service has almost doubled in just two years, freedom of information requests have disclosed.

Labour, which obtained the figures, claimed the surge in expenditure proved that every part of the NHS was at risk of being put up for sale by the Coalition Government.

The overall budget for private ambulances in England leapt from £37m in 2011-12 to £67.5m last year, a rise of 82 per cent. The most dramatic increase was in London, where spending was up by 1,000 per cent from £796,000 to more than £8.8m.

Accusations of creeping privatisation of the NHS were fuelled by reports that the agency which supplies temporary staff to hospitals faces being sold off.

Sky News said ministers were examining the future of NHS Professionals, which has some 40,000 nurses, doctors, midwives and other healthcare workers on its books. It quoted a source as saying the agency’s sale, at an estimated price of between £50m and £100m, was “a very real possibility”.

The figures on private ambulances revealed that spending quadrupled in Yorkshire and the North East to reach £3.6m and £2.9m respectively, while it went up by 143 per cent on the South East Coast to reach £13.7m.

The statistics only relate to England as health is a devolved issue in both Scotland and Wales.

Andy Burnham, the shadow Health Secretary, said: “Blue-light ambulance services have traditionally been considered part of the public core of the NHS. It is clear that no part of the NHS is now immune to privatisation.

“When people dial 999, most would expect an NHS ambulance crew to turn up. People have never been asked whether they think blue-light ambulance services should be run by private companies.”

He said that NHS paramedics had raised concerns over the training and competence of private crews and called for assurances that patient safety is not being compromised.

Labour claimed that parts of the country where spending on private ambulances spending is high were among those areas slowest to respond to 999 calls.

Citing figures from NHS England, the party says it now takes an average of 9 minutes and 56 seconds for paramedics answer a call to a patient in a potentially life-threatening state in the East Midlands, nearly four minutes longer than three years ago. Spending on private ambulances in the region has doubled over the last two years.

A Department of Health spokesman said: “Ambulances are making nearly 2,000 more emergency journeys every day than 2010, which is why we’ve employed almost 2,000 extra paramedics and provided £28m additional funding this year.

“Use of the private sector in the NHS represents only six per cent of the total NHS budget, an increase of just one per cent since May 2010.”