Britain's strategic nuclear warhead plant at Burghfield in Berkshire, has suffered up to 1000 "safety defects" in the last five years, according to figures obtained via the Freedom Information Act.

The site, which builds the bombs carried on the Trident missile submarines based on the Clyde, has only remained open because the government and the Ministry of Defence insisted it was vital to national security.

News of the faults - 300 of which were still unrepaired in April this year - are contained in 12 internal reports released by the Nuclear Installations Inspectorate (NII), the UK's atomic watchdog body.

The NII forced government scientists and engineers at Burghfield to suspend some operations on the grounds that there was a possible risk of radiation leaks, but was overruled on others in the interests of maintaining the nuclear deterrent.

Many of the problems relate to radiation-containment structures used when the warheads arrive by convoy from the Coulport armament depot near the Faslane naval base to be stripped down, tested and reassembled.

The warheads are then driven back north by road in heavily protected convoys to be reinstalled on the missiles at Coulport before being fitted back into the launch tubes of the next submarine due to leave on Doomsday patrol.

Each boat carries 16 missiles with three warheads apiece. Each warhead can be individually targeted and each is capable of destroying a medium-sized city.

One of the NII reports says a number of emergency "engineering fixes" carried out by the Atomic Weapons Establishment in response to urgent complaints had simply not worked. The report goes on to criticise AWE's "poor" and "unacceptably slow" response to safety issues and states that experience at the site "does not instill confidence that AWE's own procedures are being followed".

Kate Hudson, CND's chairwoman, said it was "shocking that warheads are being handled with anything but the highest of safety standards".

She added: "It is a national scandal that the concerns of the country's official nuclear safety watchdog have gone unresolved for several years."

Neither the MoD nor AWE's main headquarters at Aldermaston would comment.