The National Audit Office (NAO) has slammed the accuracy of Government IT savings as estimated by the Government Digital Service (GDS).

The watchdog cast doubt over the savings the Government made on IT during 2013-14, saying the GDS’s calculations were "poorly-evidenced".

The NAO’s report examined savings methods employed by the Efficency and Reform Group (ERG), a quango set up to help departments including the GDS achieve savings.

The GDS published a £91m savings figure for last yea through ‘spend controls’, but the NAO said this was a revised figure after the watchdog questioned the accuracy of its claims.

The report said: "The evidence for savings is hard to follow. There was uncertainty over some numbers with aspects of the cases still being removed or evidenced well past year-end. There were also cases where the evidence did not support the decision on whether some savings-related activities were a cancellation of previous activity or a continuation of previous activity.

"In many cases, GDS did not calculate savings correctly in accordance with the guidance and method. In some cases, not all relevant costs were included. For example, in one contract, the business case included costs for customised software support for the chosen option but they were not initially deducted from the savings."

The watchdog declined to reveal the original savings figure the GDS had arrived at, but added that because of the data the GDS required being based within the Cabinet Office, it could have "made more progress" to verify the accuracy of its calculations.

The GDS employed the same methodology in 2012-13 and its processes grew weaker last year, NAO added.

Digital transformation helped save £5m with the Department of Energy and Climate Change and £4m from the Electoral Registration.

The Government is cutting back on its IT spend with big suppliers as it tries to up spending with SMBs, largely through its G-Cloud framework.