The Ministry of Defence is failing to follow its own guidelines on assessing major procurement projects, MPs have warned.

A critical report from the Commons public accounts committee has expressed continuing concern about cost overruns at delays running into billions of pounds.

Following a review of the 20 largest projects currently underway and 10 that are currently in the assessment phase, the committee warned that the armed forces "will not receive the equipments they need when they have said they need them".

The MoD was also warned that it should "follow its own policy" on ensuring a rigorous assessment before major projects are commenced.

At present the department is spending on average less than five per cent on the assessment phase, but has said that up to 15 per cent of the initial procurement cost of a system should be spent at this stage

"One of the principles underpinning smart acquisition is to spend the right amount of time and money to reduce programme risk to an acceptable level before a project commits to the demonstration and manufacture phase," said the report.

"The assessment phase is crucial to the successful delivery of the project to time, cost and performance."

The report also said the 20 largest projects had seen cost increases of £3.1 billion over the last year, and had slipped an average of nine months beyond their expected delivery dates.

Committee chairman Edward Leigh said this was a "poor performance" by the MoD.

"The department must properly apply the sound principles of smart acquisition, and ensure that where cost overruns and delays do occur it identifies what new equipment capabilities are being foregone as a result," he said.