Republicans should not be given a last chance to join the political process, Ulster Unionist leader David Trimble has said.
David Trimble wants a return to the 1998 Agreement
Mr Trimble said that the prime minister had not taken strong enough action against them over the years.
His comments come amid calls for the government to impose penalties on Sinn Fein following claims that the IRA was behind the £26.5m Northern Bank raid.
The IRA has denied the claims and Sinn Fein backed its denials.
The Democratic Unionist Party has called for the removal of allowances and privileges at Westminster from Sinn Fein's four MPs following an assessment by the PSNI Chief Constable Hugh Orde that the IRA was behind the raid on the bank head office in Belfast on 20 December.
An early day motion in the Commons, which has been signed by Conservative party leader Michael Howard, claims that Sinn Fein can not be treated as a normal political party given its links to the IRA.
Mr Trimble, who was Northern Ireland's first minister until devolved government was suspended in October 2002 amid allegations of IRA intelligence gathering at the Northern Ireland Office, said republicans had repeatedly shunned efforts to make them purely political.
The Upper Bann MP said: "I think that what has happened over the years is that the prime minister has not been sufficiently robust.
Gerry Adams warned republicans to resist discrimination
"He has created within republicans a belief that no matter what happens they will get away with it and that if they just hunker down then eventually he will come back to them as if he was the suppliant."
Mr Trimble said that political parties needed to return to the principles of the 1998 Good Friday Agreement which brought about a power-sharing government in Northern Ireland.
He said: "We must draw a line under current experiments and go back to the
basics of the Agreement and consider, with others, where we go from here."
Mr Trimble also said that the devolution of policing and justice to Stormont must be taken off the agenda after the bank raid.
On Thursday, Sinn Fein President Gerry Adams warned republicans would resist any attempt to
discriminate against their electorate.
He said: "If the governments are going to go in the
direction of discriminating against Sinn Fein or to bash Sinn Fein, that leaves
us with no option but to defend our position.
"I am saying to republicans: let's not knee-jerk but reflect on the
"But let it be clear we will defend our electorate's rights and entitlement."