A senior clerk at the House of Commons used his work computer almost daily to download child pornography, a court was told yesterday.

Phillip Lyon also surfed at home to collect more than a thousand images of children - some performing sexual acts or having acts performed on them, Riel Karmy-Jones, prosecuting, told Southwark crown court in south London.

The Guardian today publishes for the first time detailed evidence about the alleged ring, which is said to have been based in Wrexham, and to have infiltrated local children's homes over a 20 year period.

Witnesses claim that members of the ring used their connections with police and social services to conceal their activities. All of the accused have denied the allegations.

Those named to the tribunal include:

A man who bears the same surname as a prominent Conservative supporter. Two witnesses have told the tribunal of a rich and powerful man who belonged to the alleged ring.

The son of an influential peer who admitted to police that he had been having sex with an under-age boy from one of the homes. Despite his admission, he was never prosecuted.

A powerful public official who has previously been cleared of abuse. Six witnesses have given separate accounts to the tribunal of his alleged rape of young boys. Another has reported him attending parties in Wrexham which were supplied with boys from a children's home.

Two social workers and two police officers, one of whom was accused of abuse on four separate occasions and exonerated each time, another of whom has since been jailed in another part of the country for gross indecency with a child.

More than a dozen other local men, including an executive with a local authority, a senior probation officer and a director of a major company.