The Northern Ireland assembly is on the brink of suspension or collapse as hardline unionists walk out of the power sharing government.

Democratic Unionist ministers have quit the Stormont government piling the pressure on moderate Ulster Unionist leader, David Trimble, ahead of his crunch Downing Street meeting with the prime minister today.

"The process is in such tatters and has been so undermined in terms of credibility that there can be no further participation in ministerial office," said a DUP source.

Ian Paisley's DUP have resigned from the assembly and are calling on Ulster Unionist MLAs to follow suit.

Tony Blair will urge Ulster Unionists not to turn their backs on devolved government in Northern Ireland.

The emergency talks come after Trimble said that last week's security breaches were "10 times worse than Watergate".

He is expected to call on Blair to expel Sinn Fein from the power-sharing government.

Northern Ireland's chief constable, Hugh Orde, has apologised for "serious errors of judgement" in the manner and handling of police raids on Sinn Fein's Stormont offices.

The Telegraph reveals that among secret documents "obtained by an IRA spy network" were transcripts of telephone conversations between Tony Blair and George W Bush.