The Sunday Telegraph claimed that the bugging operation was carried out by the Army's 14th Intelligence Unit, which specialises in surveillance operations. Security service sources close to the operation admitted that Dr Mowlam may not have known what she was signing the authorisation for.
It is alleged that the warrant contained only the name of the car's registered owner. The Ford Mondeo was not registered to either Mr Adams or Mr McGuinness, Northern Ireland's new Minister for Education.
Last night a Sinn Fein spokesman said: "These people [the owners of the cars] would be of no interest to the security services in their own right."
Officially the Northern Ireland Office has refused to confirm any involvement on the part of the security services, police or Army in the operation, but no police inquiry has been launched.
In a further controversy, Sinn Fein is to press for Northern Ireland's new ruling Executive to remove all Union flags from public buildings in the province. The republican leadership is also calling for symbols associated with the Unionist tradition, such as portraits of the Queen, to be banned from workplaces.
The proposals, which are bound to cause fury in Unionist quarters, are among the recommendations made in the party's programme for government, due to be released this week. It is understood that the party will recommend to Stormont's power-sharing Executive that where Union flags and Unionist emblems - such as the Red Hand of Ulster and the Crown - are not removed, the Irish tricolour and nationalist symbols should be put up alongside them.
Apart from government departments, the public bodies that could be affected by the proposal include the province's fire and ambulance services.
The Ulster Unionist MP Jeffrey Donaldson warned Sinn Fein last night that it would be undermining "a central tenet" of the Good Friday Agreement. "I think here we have evidence of Sinn Fein's strategy to advance their own very narrow agenda of removing the British identity from Northern Ireland," said the Lagan Valley MP.Reuse content