Security has been stepped up at the UK's nuclear power stations, the Department of Trade and Industry has confirmed.

The DTI plans to bring in more rigorous security checks for all new and existing staff after a review of procedures.

The move comes after a guard attempted to hack into a computer system at one nuclear site, the Guardian reported on Tuesday.

The security guard is alleged to have made efforts to alter sensitive information contained on computers at the unnamed complex.

'Undisclosed convictions'

The patrolman had never been vetted and he had two undisclosed criminal convictions, according to the newspaper report.

The scare is believed to have taken place at the Bradwell magnox reactor in Essex, the nearest nuclear power generator to London, it is reported.

A DTI spokesman confirmed that security had been revised in response to an incident but he refused to divulge details.

"There has been an incident which did not cause a breach in security," the spokesman said.

'Revised procedure'

"It caused a review of security and in light of that review a revised procedure is to be introduced in March."

The Guardian says it has obtained copies of leaked DTI memos written by Peter Hatton, head of security in the government's office for civil nuclear security.

In the memos Mr Hatton describes the incident, which happened in June 1999, as the "deliberate action of a member of the site security force".