David Trimble is facing a new challenge from hard-line Ulster Unionists intent on wrecking the Good Friday Agreement.

A meeting of Ulster Unionist party managers on Friday has delivered a double blow to the moderate unionist and Stormont first minister - and could pose a threat to Northern Ireland's troubled peace process.

Two anti-agreement Ulster Unionist MPs sought and won permission for a dual mandate - allowing them to run in Northern Ireland's assembly elections.

Lagan Valley MP Jeffrey Donaldson and South Antrim MP David Burnside are now allowed the right to run for Stormont.

And party officials agreed to an anti-agreement unionist demand for the UUP's ruling council to debate whether the party should remain in the power-sharing Stormont executive with Sinn Fein.

The 860-strong council will convene on September 21 as Trimble is forced for the ninth time since the signing of the Belfast Agreement to debate power sharing.

Trimble supporters regard the move as a bid to bring down the Ulster Unionist leader and the Stormont executive.

"We are regarding this as a leadership challenge," said an aide.

"If the assembly and the institutions are torn down, we are left with a very uncertain world -- possibly a very violent world. I would take these people more seriously if I thought they were genuine about power-sharing."

Some believe the bid by hardliners to run for both the Commons and Stormont raises the game by the UUP's anti-agreement wing.

Currently the only Westminster MP to sit in the Stormont assembly is UUP leader, Trimble - who is first minister in the Northern Ireland assembly.

The first minister's grip on Stormont is tenuous, with the UUP holding 26 of 108 places.

Trimble faces the constitutional requirement to build cross community consensus with the nationalist SDLP.

If the two hard-line MPs enter the assembly, Trimble's role as coalition builder would be severely tested.

SDLP leader Mark Durkan and deputy first minister warned hard-liners not to think they could negotiate a better agreement by collapsing the power-sharing Stormont executive.

He cautioned the UUP that its "soap opera politics" were playing into Paisley's hands and threatening the peace process.

"The DUP's efforts to strengthen itself are aided and abetted by all that is going on inside the UUP. The contest between pro and anti-agreement elements on who can provide the best threat to the institutions is in danger of becoming a leapfrog onto quicksand," he said.

Some suggest Trimble gave dispensation for Donaldson and Burnside in order to defuse their opposition to the Good Friday Agreement.

Former UUP MLA, Peter Weir, who switched to the DUP, argues the pair will be co-opted to show a united front in the face of a strong electoral challenge from the Reverend Ian Paisley's party.

"To have any chance in the election, David Trimble needs both to present the facade of a united party and to appeal to at least some anti-agreement voters," he told Ulster TV.

"He is desperate for Jeffrey Donaldson and David Burnside to run to help him achieve this. Sadly by putting their names forward they are playing into his hands."

Paisley's DUP will call for the agreement to be renegotiated if his party overtakes the UUP at next May's elections.

Insiders predict that Donaldson stands a fair chance of being returned to Stormont in an anti-agreement ticket, they warn Burnside that he is unlikely to win in his more moderate constituency.

UUP sources say that the prospect of multiple mandates arouses "discontent" in the party.

The party's rank and file have questioned how MPs and MLAs, who also sit on Westminster committees, can represent ordinary Ulster people.

The UUP has frequently criticised Paisley who sits in Stormont, Westminster and in the European parliament.

Donaldson sits on two select committees and is party spokesman on the Treasury, transport, work and pensions.

Burnside sits on one select committee and is UUP spokesman on culture, environment and defence.