Fears have been raised about the backdoor privatisation of the region's ambulance service after it emerged one major contractor is underpinned by the billionaire shareholders of Aston Martin.

An investigation by The Eastern Daily Press into the millions of taxpayers' pounds spent by the East of England Ambulance Service Trust (EEAST) on private ambulances has found that NHS money is benefiting one firm which is part owned by a £3-billion investment fund called InvestIndustrial.

The Italian conglomerate bought a 37.5pc stake in Aston Martin in December for £150m and in February one of its subsidiaries bought east of England ambulance provider Thames Group.

The EDP has traced paperwork across the continent which shows how a trail of six different firms in Britain, Spain and Luxembourg lead from East Anglia to Italy.

The money is paid from the EEAST to one of the region's biggest private ambulance providers, Thames Group, which received £340,000 in March from the trust.

The firm was sold in February after its chief executive, Rob Ashford, reported a 'fantastic' 2012.

In the last year Thames Group has received more than £1.3m from the ambulance trust for private vehicles.

Documents registered at Companies House show the new owners of Thames Group is a firm called UK Ambulances 2, based in Doncaster, whose directors are Stefano Pellegri and Margaret Serna.

Its directors, owners and address are the same as a firm called Premier Care Direct Ltd which is owned by a company in Barcelona called Supsar Invest SL.

The Spanish company is owned by a firm based in Luxembourg called Emergency International Invest Sarl.

And the Luxembourg firm is, in turn, a subsidiary of Italian investment fund InvestIndustrial.

This complex web of corporate ownership linking firms receiving NHS money to Aston Martin has angered health campaigners.

When told by the EDP about the trail of ownership, Gary Applin who is branch secretary of Unison for EEAST said he was 'speechless'.

He said: 'Why are we spending money on private ambulances when we could be spending on our own people?

'It is scary and frightening and makes me angry.

'I'm stunned. This is privatisation rearing its ugly head. It is totally against my doctrine and that of the NHS.'

Denise Burke from North Norfolk Labour Party's Act on Ambulances campaign said: 'It is shocking enough that EEAST has to rely on private ambulances which are often not adequate to meet patients' needs, but even more shocking that NHS funding is being used in this way when it should be going on our front-line paramedics.

'Commissioners should be held to account to use NHS funding properly.'

On May 7 the EDP reported through the Ambulance Watch campaign, that more than 200 front-line vacancies had been left unfilled at the trust for years, while spending on six private ambulance providers had soared to almost £13m in 17 months.

The EEAST is now trying to reduce the amount of money it spends on private ambulances as part of its turnaround plan after admitting it had become too reliant on them.

The turnaround plan was announced by interim chief executive Andrew Morgan at the end of April.

A spokesman for the trust said: 'We are looking to reduce our spend on private ambulance services so that the money can be re-invested in our front-line service.

'Our turnaround plan details how, by reducing the spend on such providers, recruiting staff, reducing sickness and investing more in our emergency operations the trust will be looking to consistently staff the equivalent of an additional 25 24/7 NHS ambulances.

'These will be on top of the circa 170 ambulances the trust currently deploys at peak times of the day.

'All private ambulance services are procured according to NHS regulations in the same way that we purchase all of our equipment and consumables.'

But the trust declined to comment when asked if it was tied into long-term contracts with private ambulance providers which would make it difficult to reduce spending on them.

Health minister and north Norfolk MP Norman Lamb urged the EEAST to follow through on its plan to reduce its use 'excessive' use of private ambulances.

'This (spending on private ambulances) is not being driven by the government,' he said. 'There is no encouragement from the government.

'They (the EEAST) behave in this irrational way. It is crazy to freeze recruitment and hire private ambulances.'

Chairman of Thames Group Margaret Serna said she wanted to expand the private ambulance service after February's takeover.

She said the firm was investing in ten new ambulances worth £100,000 each which are specially adapted to take patients weighing up to 50 stones.

'Andrew Morgan has a turnaround plan but it takes time to implement these things,' she said.

'We also have an exciting project at Ipswich Hospital where we put paramedics into the A&E department and they help triage patients.'

She added: 'There is an issue around investment and access to funding in the NHS. It is difficult to access funding. We have that and we can implement projects more quickly.'