Jeffrey Donaldson, MP for Lagan Valley, has been told he cannot stand for the forum on a UUP ticket.

He failed to win dispensation from party officers required before an MP can sit in another body.

He walked out of Northern Ireland's all-party talks in April hours before a consensus was reached on Good Friday.

Defied leadership

He went on to campaign for a No vote in the May referendum, embarrassing his party leader, David Trimble, who backed the accord.

When the agreement was accepted with a resounding majority, Mr Donaldson switched allegiances again and called on the UUP to unite.

Party officers

But around a dozen senior party officers took the decision to prevent him running for the Assembly, citing the official reason that he was already a Westminster MP.

The UUP has decided only Mr Trimble and his deputy, John Taylor, will be allowed to mix both roles.