Watchdog warns on Trident timing

HMS Vanguard: Trident submarines will last until mid 2020s

Critical decisions must be taken urgently on replacing Britain's nuclear weapons system if it is to be ready in time, says the National Audit Office.

The spending watchdog warned of a "challenging timetable" if the new submarines were to be ready before the old Vanguard class was retired in 2024.

Key developments would have to be made by September 2009, if the project is to remain on course, it said.

Ministers agreed it was challenging but said the project was on schedule.

The Trident system - made up of submarines, missiles and warheads - are due to end their working lives in the 2020s.

'Good progress'

Former prime minister Tony Blair gave the go-ahead to replace the system in 2006, which was estimated at the time to cost between