Tony Blair should consider taking away Sinn Fein's Westminster offices to help restore trust in the Northern Ireland peace process, Tory leader Iain Duncan Smith is expected to say.

In a speech on Saturday, Mr Duncan Smith will also urge the prime minister to back up with actions his "tough" message to republicans.

In the wake of the suspension of power-sharing at Stormont, Mr Blair on Thursday called for an end to the IRA.

Sinn Fein's four MPs moved into offices in the House of Commons in January this year despite their refusal to sit in what they regard as a "foreign" Parliament.

The Tories opposed the move, saying Sinn Fein was getting a London propaganda and lobbying base at taxpayers' expense, without giving any commitments in return.

'Tough action needed'

Now Mr Duncan Smith is taking up the issue again as he addresses the Ulster Unionist Party's annual conference.

He will say Mr Blair has delivered tough words before to parties in Northern Ireland.

"Too often, in the past, resolute words from the prime minister have been followed by irresolute action," he will say.

Duncan Smith: Too many one-sided concessions

"The prime minister now needs to deliver and follow through. I will support him if and when he does."

Mr Duncan Smith will argue that giving Sinn Fein Westminster offices is among "one-sided and unnecessary concessions" which have undermined previous tough words.

"In the light of Sinn Fein's behaviour at Stormont, this special status must be reviewed," he will continue.

"Along with breaches in the ceasefire, this has done more than anything to give the impression that the process is a one-way street and to undermine confidence in it.

Police worries

"It is time to restore balance to the process. It is time to ensure that rewards follow performance and that breaches are properly sanctioned."

The Tory leader will say further reforms to the "already demoralised and under-resourced police", planned for the autumn, are other examples of one-sided concessions.

"It is time to insist that all parties operate on a level playing field and under the same rules," he will say.

That means a comprehensive agreement, with "strict linkages and a clear timetable", on how to put the Good Friday agreement into action.

The agreement is the basic template for a political settlement, he will argue, but that has to be on the terms agreed by the people of Northern Ireland four years ago.

Republican anger

Mr Duncan Smith will also stress the need for an end to private armies and paramilitary activity and the IRA must give "an unequivocal declaration that the war is over".

Sinn Fein President Gerry Adams has said republicans were angered by Mr Blair's speech.

Deadlines had not worked in the past, argued Mr Adams.

"What we need to do is to understand that the removal of the political anchor of the process was a grievous mistake," he said.

Mr Adams pressed for new all-party talks and an end to the suspension of devolution for Northern Ireland.