Sinn Fein is to show Mr Tony Blair a bugging device which it claims to have uncovered in one of its offices, party president Mr Gerry Adams said tonight.
Mr Blair will be given the sophisticated device on Thursday at crunch talks on the future of the Northern Ireland peace protest, said Mr Adams.
The listening equipment was found in Sinn Fein's Connelly House offices in Andersonstown by workmen carrying out renovation work, said the party.
The discovery came a week after an earlier find at the home of a member of Mr Adams staff, said republicans, and after he ordered a security sweep of people's homes and offices.
Mr Adams accused the government of a "gross violation" of his party's rights.
As he prepared to leave for Leeds Castle for three days of crucial talks starting on Thursday with the other Northern Ireland parties, and chaired by Mr Blair and Taoiseach Bertie Ahern, Mr Adams said he was taking the bug with him.
"It is not just a matter of showing it to the Prime Minister, it is a matter of returning it to the Prime Minister. It is a matter for him to decide if this is the way to proceed - if he hasn't authorised it, who has?" said Mr Adams.
The talks are the latest effort to find a way of reaching an agreement to restore devolution to Stormont and Mr Adams said of the bugging device "this is not the way to make peace. The British make it very, very hard to make peace when this goes on."
The bug was hidden under the floor of a first floor office with microphones pointing into the office and down into a conference room below, said Sinn Fein.
Party chairman Mr Mitchel McLaughlin said it was a highly sophisticated device with a large battery pack and the party had no idea how long it had been in place.
The device, five foot three inches long, was disguised as a floor joist and discovered last night, he said.
Sitting behind the device at a hastily arranged press conference in the room where Sinn Fein said it was found, Mr Adams accused the government of bad faith.
PA