THE Prime Minister will be in Northern Ireland today urging the electorate to give a huge Yes vote in the referendum on the Ulster peace agreement.

Former Prime Minister John Major will join Tony Blair him on the campaign trail.

Political differences put behind them, they are due to share a platform standing shoulder to shoulder calling on the Ulster people to take what Mr Blair has called the best chance for peace in Northern Ireland in decades.

Mr Blair, who today celebrates his 45th birthday, is due to return again shortly before the May 22 referendum with current Conservative leader William Hague and Liberal Democrat leader Paddy Ashdown.

Yesterday the United Unionist No offensive, the non-party Yes Campaign and the loyalist Progressive Unionist Party, calling for backing for the Good Friday agreement, all moved into top gear.

The independent Yes Campaign called in the assistance of top advertising agency Saatchi & Saatchi, who designed their billboard campaign free of charge.

The United Unionist No campaign was formally launched with a claim that backing for the Good Friday deal would put Northern Ireland on the road to a united Ireland.

Meanwhile, the transfer of six long-term IRA prisoners from Britain to a jail in the Irish Republic was welcomed last night by Sinn Fein. Mr Martin Ferris, a senior figure in the party's policy-directing executive, also said the move was ''long overdue''.

The IRA group - including the so-called Balcombe Street gang, jailed in London more than 20 years ago and two convicted killers - were flown back to Ireland in a high-security operation yesterday.