BBC Defence Correspondent Mark Laity explains how the scandal was discovered

Military investigators are reported to have found 170,000 pornographic images downloaded from the Net during a routine security check.

A member of staff at the Ministry of Defence research laboratory has been suspended for downloading the material.

The worker is based at the Defence Evaluation and Research Agency, Dera, at Malvern, Worcestershire.

The MoD confirmed the suspension of its employee together with those of four employees from another company who were carrying out work at the laboratory.

The matter is almost certain to be raised in the parliament on Monday, when the defence minister faces MPs.

Liberal Democrat foreign affairs and defence spokesman, Menzies Campbell, said: "The real issue here is not the fact that it was porn that was downloaded but the fact that the MoD computer system could be manipulated so easily.

"So far as we know, security was not compromised on this occasion but it is absolutely essential that suitable procedures be put in place to prevent abuse of this kind in the future."

Downloading round the clock

More than 170,000 images were allegedly found

MoD police discovered staff had used a special program to collect the images around the clock from sexually explicit Websites.

The government scientists, who are behind battlefield technology for the armed services, used 200 false identities to collect the images.

The images were allegedly downloaded in just three weeks.

'Valuable resource'

The files were collected throughout the day

The investigators found a key computer, which should be used to communicate with colleagues worldwide, had spent 70% of its online time downloading and distributing pornography.

Rupert Cazalet, a spokesman for Dera, said an investigation was under way to determine whether disciplinary action will be taken.

He said: "A number of pornographic images were discovered and that is why one Dera staff member and four others were suspended.

"To access or download material which is not work related is a disciplinary offence.

"The monitoring of Internet communications is being tightened as a result but we are aware that the Internet is a very valuable resource.

"However, we understand that sometimes temptation gets the better of people like in any big organisation."

More than 3,500 Dera employees across Britain had access to the system containing the material, it was reported.

Jim Bates, a forensic computer expert who carried out an independent inquiry, told The Sunday Times: "The sheer amount of material is staggering. I've never seen anything with such huge quantities relayed to such large numbers of people."

One member of staff appeared in court in connection with the affair, but was acquitted, Mr Cazalet said.