MI5 hunts IRA spy

Senior MI5 officers will be sent to review security at the Northern Ireland Office amid fears that an IRA spy is still operating.

Police and security sources believe that the full extent of the Provisionals' intelligencegathering activities at Stormont has yet to be revealed.

Tony Blair is set to face questions on the crisis in the peace process in the Commons today. The Prime Ministerwas meeting hardline Unionist Ian Paisley for talks.

The discovery of an alleged IRA spy ring at Stormont two weeks ago triggered a breakdown in trust between Unionists and republicans which led to suspension of the devolved government, announced
by Ulster Secretary John Reid yesterday.

When he told the Commons of MI5's involvement, it was presented as a root-and-branch security review to stamp out further breaches. But security sources told The Times that at least one agent may still be in place and undetected.

They said documents seized from IRA suspects included a list of prison officers' names dated as recently as this March.

Police have seized up to 1,000 papers from the homes of republicans and Sinn Fein offices at Stormont.

Four people have been charged with possessing information useful to terrorists.

Up to 2,000 prison officers are now thought to be under threat because of the breach. Unionist leader David Trimble cliamed the taxpayer faces a bill of up to £90 million to rehouse them.