Sinn Fein is expected to campaign for a Yes vote in the Ulster and Irish referendums on May 22. Mo Mowlam, the Northern Ireland Secretary, welcomed the vote: "I recognise how significant this decision is for republicans and pay tribute to the leadership of Gerry Adams in bringing his party to support the agreement." The vote piles the pressure on David Trimble, leader of the Ulster Unionists.

Six of his 10 MPs are against the deal, and he is struggling to break the momentum which appears to be building in the No campaign in the Protestant community.