Sinn Fein has put on show a "sophisticated bugging device" which it said was found in the home of a party member in west Belfast.
The device was found in the living room ceiling
Party sources said it was found by workmen in the Andersonstown home of a woman who works at party president Gerry Adams' constituency office.
The listening device, found in the living room ceiling, consists of a number of battery packs, along with a microphone and transmitter.
The discovery came as the parties were finalising their positions for next week's intensive political talks at Leeds Castle in Kent.
In a statement Sinn Fein said the device was being used as part of a British spying and intelligence gathering operation.
"It is clearly the work of a British State agency and is part of a spying and intelligence gathering operation," it said.
Mr Adams said he would raise the incident with the government.
Sinn Fein Assembly member Michael Ferguson said the incident was "shameful and despicable".
The Northern Ireland Office refused to comment in response to the allegations.
The party has been at the centre of bugging allegations a number of times before.
Mr Adams said in December 1999 that one was planted in a car used to transport himself and chief negotiator Martin McGuinness during the Mitchell Review.
In April 2003, the Times newspaper published what were said to be transcripts of secretly recorded telephone conversations between Mr McGuinness and senior government officials.
BBC Northern Ireland security editor Brian Rowan said that ahead of crucial talks at which the future of the IRA will be a key part of the agenda, Sinn Fein would use this latest discovery as evidence that the British intelligence war is far from over.