A multimillion-pound software blunder by the Ministry of Defence (MoD) in its procurement of Chinook helicopters has deprived troops in Afghanistan of better air support and "potentially put the lives of British service personnel at greater risk", according to a damning report.

The Commons Public Accounts Committee (PAC) condemned the way the MoD handled the purchase of eight Mk3 helicopters from Boeing in 1995 without ensuring access to software code that is essential to certifying airworthiness.

Painfully slow progress was made in downgrading the Chinooks to enable them to be certified under a since-abandoned "fix to field" programme involving five years of negotiations with Boeing. None of the choppers have yet been put into service.

The committee said: "The absence of these helicopters has meant that British troops in Afghanistan have had to make do with fewer helicopters, make an increased number of dangerous journeys by road and, due to the specialist nature of the Mk3, rely on heavily modified Mk2 helicopters for use on high-risk special operations. The modification of the Mk2 Chinook cockpit to enable their use in low-light conditions was a far from perfect solution and compounded safety risks."

The cost of the helicopters has soared 70 per cent to £422m, or £52.5m each. Alternatives available when the order was placed "may have been cheaper", said the report.

The MoD has since moved from "fix to field" to a new "reversion" project drawn up without consulting Boeing.

Defence equipment minister Quentin Davies said he "entirely accepts the criticism that successive reports have made," but claimed there was "nothing new " in the latest PAC report, ignoring the disclosure that the new reversion programme has been adopted to get the machines into the air without checking costs with Boeing, resulting in an even higher bill.

Davies said the Chinooks were "a very bad case" and would remain "a lesson to us all".

The MPs said that "given that software is key to the operation of most modern defence equipment", it was "irresponsible" not to have made it a contractual requirement.

"The department should specify access to software as a clear requirement within any contract, especially where access to proprietary software is needed to provide airworthiness certification," they said.

Committee chairman Edward Leigh said: "The programme was hamstrung from the start by the appalling decision to buy the aircraft without securing access to their software source code.

"This meant that the MoD could not show that the cheaper, modified cockpit avionics which it had chosen met UK airworthiness standards and hence that the helicopters were safe to fly. ""

The Chinook Mk3 fleet was grounded because the contract with Boeing did not specify that software documentation and codes for avionics systems should be analysed in accordance with UK defence standards.

As a result, it was not possible to demonstrate that the helicopter’s flight instruments meet the required standards. So, instead of providing heavy-lift capacity to British troops, the choppers have spent nine years in RAF hangars.

The government said in January last year that it was to spend another £90m rectifying the software and avionics problems.