The prime minister will this week ask Ulster Unionists not to "bring down" the Northern Ireland peace process.

David Trimble has called on the government to act against republicans after police raided Sinn Fein's offices in the Stormont assembly.

Officers have charged a senior Sinn Fein official with having personal details of the British Army's General Officer Commanding in Northern Ireland.

In a Downing Street meeting later in the week, Tony Blair will plead with the Ulster Unionist leader and Northern Ireland first minister not to tear down devolved power-sharing institutions and to save a peace process in crisis.

Ulster Unionists claim Sinn Fein led a republican spy ring at the heart of the Northern Ireland government.

There are allegations that republicans gained access to British government negotiating positions - giving Sinn Fein the whip hand in talks.

It is also feared that paramilitaries may have details of MI5 informers and agents.

Blair will ask Trimble to wait for two weeks - until Number 10 investigates the claims against Sinn Fein - before responding.

The PM will ask him not use the "nuclear option" of quitting Stormont - a move that would bring down the Good Friday Agreement - ahead of Downing Street talks with Irish leader Bertie Ahern and republicans.