DUBLIN (Reuters) - Support for Irish Prime Minister Bertie Ahern`s party has hit a record of 63 percent ahead of a landmark referendum on Northern Ireland, an Irish Times/MRBI poll reported on Monday. Ahern`s Fianna Fail, which strongly supports a `yes` vote for a Northern Ireland peace plan on May 22 , is now more popular than any Irish party in the past 25 years, the paper said. Other surveys have suggested that the electorate will agree to Ireland amending its constitution to drop its territorial claim on Northern Ireland, as it must if the peace deal is to survive. Support for Ahern`s party was higher than the 57 percent backing it won after Ahern helped broker the peace deal on April 10. MRBI said it had questioned 1,000 voters at 100 sites across Ireland last Tuesday and Wednesday. It showed that backing for the Irish Republican Army`s political allies in Sinn Fein had three percent support - a drop of one percentage point since the poll was last conducted in mid-April. The main opposition party, Fine Gael, is also campaigning for a `yes` on May 22, which needs a simple majority to agree for it to be carried. The prime minister`s rating rocketed to 84 percent after he put aside the personal tragedy of his mother`s death in the final week of the talks, flying back and forward between Dublin and Belfast to attend the funeral and participate in the negotiations on the same day.