Sinn Féin has accused British security forces in the North of bugging the home of a peripheral member of party leader Gerry Adams' staff.
As Adams and his deputy Martin McGuinness were meeting British officials in London, Sinn Féin held a news conference to display a "sophisticated bugging device" which the party said was found hidden in the unnamed woman's home.
"Gerry Adams and our negotiators are in London trying to move the peace process on, and here we are in Belfast where we have the intelligence services operating with impunity, 10 years after the IRA ceasefire," said Sinn Fein's Michael Ferguson on Monday.
"It's fairly clear their intentions aren't about promoting the peace process, and actions like this do anything but support and move the peace process on. It's ridiculous, it's shameful."
A spokesman for the Northern Ireland Office declined to comment on the allegations.
The alleged find comes at a sensitive time for the Northern Ireland political process, which has been deadlocked since October 2002 when London suspended a power-sharing provincial government, set up under the 1998 Belfast agreement, following allegations of IRA spying.
Intensive talks aimed at reviving home rule and securing the full disarmament of the IRA will be held in England next week.
The device displayed by Sinn Féin consisted of a number of battery packs, wires, a transmitter and what appeared to be a microphone.
The party said the batteries and transmitter were found by workmen this morning in the roofspace of a house in Andersonstown with the microphone concealed in the living room ceiling.
The woman who lives there is not a senior member of staff, the party said, but carries out a few hours voluntary work each week in Adams' constituency office.
It is not the first time Sinn Féin has alleged it has been bugged by London. Former Northern Ireland Secretary Mo Mowlam has since admitted she authorised the bugging of a car used by Adams and McGuinness during talks in 1999.