Described as a section of an "MI5 British spy device", it is being sold on the online auction site, eBay, accompanied by a framed, handwritten letter from party president Gerry Adams.

The device was said to have been discovered at Connolly House in Andersonstown in September 2004.

At the time, the party said the device had two microphones - one directed at an office, the other at a meeting room.

However, the device no longer works and is being sold as an historical artefact. There are about 12 bidders with the highest offer exceeding US $800.

"This is a unique opportunity," reads the description on eBay.

"A historical item such as this has never before been made available and it's highly unlikely that it will happen again."

In the accompanying letter, Mr Adams says MI5 admitted bugging the Sinn Fein office.

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He says he and party colleague Martin McGuinness gave part of the bugging device to Tony Blair during political talks in Leeds Castle in Kent that same month.

Mr Adams adds: "When we were leaving that meeting I held on to a section of that device.

"Since then I have been in correspondence with various elements of the British system to establish who authorised this electronic surveillance operation.

"In January 2005, Eliza Manningham-Butler, head of MI5, admitted that MI5 bugged Connolly House.

"This note is authentication by me that the section of the bugging device which it accompanies is part of the Connolly House device which was returned to Mr Blair."

A Sinn Fein election poster, featuring Gerry Adams, is also for sale on eBay.

Its description reads: "This is an original Sinn Fein 2005 election poster seen around the north of Ireland and in west Belfast.

"It is approxinately three and half feet by two and a half feet. Some haven't been used and some are straight off the lamp posts of west Belfast."