Raids on £30 million worth of suspected IRA property in Manchester could destroy new attempts to restore devolution in Northern Ireland, unionists warned.
Anti-racketeers searched 250 homes and businesses as part of a huge financial investigation linked to Tom "Slab" Murphy, the Provisionals' alleged chief of staff.
The Assets Recovery Agency (ARA), backed by police and authorities in the Irish Republic, launched the offensive after receiving clearance at the High Court in London.
Two Manchester-based businessmen, including Dermot Craven, a landlord and scaffolding boss, were at the centre of the probe.
Officers moved in as Sinn Fein leaders Gerry Adams and Martin McGuinness prepared for Downing Street talks with Prime Minister Tony Blair.
With decommissioning chief General John de Chastelain declaring just ten days ago that all IRA weapons had been destroyed, the meeting was to focus on a fresh push to revive the power-sharing administration in Belfast. But as Mr Adams railed against those peddling a political agenda, unionists insisted the development could have grave consequences.
Their trust in the IRA abandoning all crime, including international moneylaundering operations, was wrecked by the £26.5 million heist at the Northern Bank's Belfast HQ last December.
Danny Kennedy, deputy leader of the Ulster Unionists, declared: "If, after investigation by the ARA, the properties turn out to be linked to the IRA, this will have very serious consequences for the political process in Northern Ireland.
"The extent of the IRA's vast criminal empire was confirmed by the Northern Bank robbery.
"The republican movement is probably the largest organised crime network in the British Isles."
Boxes of documents seized during the raids across Greater Manchester were being studied last night by ARA officials.
Part of the probe centred on Craven Properties in Sale, run by Mr Craven. Police also went to his £2 million gated mansion in the exclusive village of Bowden, neighbours said.
Mr Craven and his wife Dawn were seen at the Victorian property.
In a statement the ARA confirmed domestic and business addresses owned by two men and worth £30 million were searched.