Channel 4 News said a tower in Capenhurst, Cheshire, was used to intercept all telephone signals between Ireland and the UK from 1989 to when it closed down earlier this year.

Channel 4 said sources claimed the tower was used for "anti-terrorism" purposes

The 13-storey windowless tower used electronic equipment to collect and store all faxes, e-mails, telexes and data communications, the programme said. Their contents were then allegedly scanned for key words and subjects of interests.

The report said the tower was situated in north-west England, directly between British Telecom towers sending messages to Ireland.

Channel 4 said sources told the programme that "although the primary justification for building the tower was anti-terrorism, the information it gathered was also of economic and commercial significance".

A Home Office spokesman said the government does not comment on "alleged interception activity", which is "in accordance with standard practice".

For sale

"Under the Interception of Communications Act, interception of any communication on a public telecommunications network in the UK requires a warrant to be signed by the Secretary of State," he said.

"Where someone believes their communications have been intercepted in breach of the Act they can take their case to an independent tribunal or to the police.

"There have been no successful challenges to the Act in the European Court of Human Rights."

The tower has now been put up for sale by the Ministry of Defence for about �20m.