Software, hardware and other technical problems cost the Ministry of Defence an extra £88m and 19 months of delays to key defence projects in the last year, according to the National Audit Office (NAO).

The Major Project Report 2001 covers the period to 31 March this year, and provides cost, time and technical performance data on the top 30 defence projects.

It revealed that rapid changes in computer hardware have cost the Eurofighter project £33m in obsolescence costs.

The Eurofighter is designed for air superiority and will allow the RAF to replace the Tornado F3 and Jaguar. The first fighter is due to be delivered to the RAF next June.

Technical problems are also to blame for slippage in the project for the Advanced Short Range Air-to-Air Missile (Asraam), resulting in an additional £25m in interest on capital charges.

Technical factors resulted in 19 months of delays to three projects, adding six months to the Asraam project and one to the Attack Helicopter project. The report noted: "The 12 months slippage in the Swiftsure and Trafalgar Class Submarine Update was caused by software engineering problems which led to the sonar system development programme being delayed."

But the NOA said this year's projects have performed the same or better than last year, and costs and project slippages are under better control.