The NHS Litigation Authority has greatly increased its use of surveillance by private detectives to investigate suspect claims, new figures have revealed.

A freedom of information request to the authority by the Gazette shows that it commissioned private investigators 24 times in 2013/14, up from 10 times in 2012/13. In 2010/11 they were used just once, to investigate a clinical negligence claim.

Figures so far this year suggest a continuing upward trend: by mid-October, the body had commissioned detectives 16 times since the start of April.

In 2013/14, the first year that figures were calculated, the NHSLA spent £49,600 on detectives. To date this year, the sum is £14,725.

The evidence shows that most of the time, investigations do not reveal that a claim is fraudulent or exaggerated. In 2013/14, 58% of investigations uncovered no wrongdoing; the figure for 2012/13 was 60%.

The authority estimated that it saved £3.7m in 2013/14 by the use of private detectives. The figure was calculated by comparing the cost of the final payout of claims against the pre-surveillance damages reserve predicted by the panel firms used.

The organisation is authorised to conduct investigations into claimants’ injuries through its published surveillance protocol.

Authorisation to investigate suspect claims expires after three months and the reasons must be stated in writing. Investigators can only be commissioned to prevent or detect fraudulent claims, or if it is in the interest of the taxpayer.

According to the protocol, the chief executive must be satisfied of the nature of the surveillance and the details of any potential intrusion into people’s privacy other than the claimant, as well as the steps taken to minimise this risk.

The Gazette asked the NHSLA for an example of an investigation uncovering fraudulent behaviour and was pointed to a 2010 case involving a £3m claim for spinal injuries following alleged medical mistakes.

Detectives secretly filmed the claimant for three months and recorded him playing golf and lifting a mini-motorbike into the back of a car. His compensation was reduced to £190,000.

The authority’s annual report, published during the summer, showed that the number of new clinical claims rose by 10.8% to 10,129 during 2012/13. The figure has increased by 66% in the past four years.