A report on Channel 4 News said the calls were intercepted at a specially built communications tower at Capenhurst, Cheshire. The operation only stopped when the facility was closed down earlier this year. The tower is now on sale.
While the operation, which was started in 1989 under Margaret Thatcher's premiership, was defended on the grounds that it was used to counter terrorism, the information gathered also had economic and commercial value.
Yesterday Mr Reynolds, Irish prime minister between 1992-94 when the evolution of the peace process was at a key stage, said the eavesdropping was an "outrageous incursion into the sovereignty of the Irish state". He added: "[It was] a total breach of faith between friendly governments that were, during that time, carrying out initial discussions on the peace process.
"There were times during those discussions when I had a question mark in my mind, but I had nothing to go on."
Gay Mitchell, foreign affairs spokesman for the Fine Gael opposition party, said the reports were disturbing and called for a full explanation from London.
"This is not only an offensive act, it has commercial as well as political implications," Mr Mitchell said.
Patricia McKenna, an Irish Green Party member of the European Parliament, said: "Such a situation poses alarming consequences not just for the basic civil liberties of the Irish public, but also for the economy."
Of particular concern is that the intercepts related not just to terrorist- related matters but to items of commercial and economic interest.
One incident attracting suspicion was possible advance warning to London of Dublin's bottom line in the currency crisis which undermined the Irish punt between September 1992 and January 1993.
Channel 4 News said the windowless, 13-storey tower at Capenhurst contained electronic equipment to collect and store all faxes, e-mails, telexes and data communications. It is alleged that the contents of the intercepted communications were scanned for key words and subjects of interests.
When the tower was erected in 1989, the Ministry of Defence held a meeting with local residents and urged them not to talk about the site. In return they were given free fencing and double-glazing.
Yesterday a Downing Street spokeswoman said she was not aware of any representations from the Irish Government.
A Home Office spokesman said: "In accordance with standard practice, the Government does not comment on alleged interception activity.
"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.
"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."
He added: "There have been no successful challenges to the Act in the European Court of Human Rights."Reuse content