Belfast

THE Prime Minister is due to make a final, personal appeal today for a Yes vote in Northern Ireland amid mounting tension over the growing strength of the No campaign amongst Protestants.

An opinion poll published yesterday revealed only 52% of the population intended to vote Yes, well short of the crucial 70% target identified by Northern Ireland Secretary Mo Mowlam.

The poll's principal finding was also worryingly overshadowed by the suggestion one quarter of all voters had yet to decide which option to support, while 35% of Ulster Unionist Party supporters had yet to make up their mind before Friday's referendum.

With uncertainty running so high, Mr Tony Blair moved yesterday to underline his commitment to securing a Yes vote on Friday - an achievement he said would give the province a ''far better chance'' of clamping down more strongly than ever on fringe terror groups.

As Mr Blair delivered his message, Irish tourist offices worldwide were put on alert after an explosive device was delivered through the post to the headquarters of Dublin Tourism.

No group immediately claimed responsibility but there were clear signs of an Ulster paramilitary link. The device, apparently mailed from the North, contained a small tube of explosive material and was packed in a video case with ball bearings.

Only hours earlier, Mr Blair had said while he understood concerns over the release of prisoners and proposed reforms of the RUC, he did want to give those allied to the main paramilitary groups, who signed to the peace deal, the chance to ''cross the bridge and come from violence to democracy''.

During an hour-long phone-in on BBC Radio Ulster, he also issued a thinly-veiled warning against voting Northern Ireland's hardline No campaigners into any future Stormont assembly.

''If we elect people to the assembly who are intent on wrecking it, there is nothing any politician can do,'' Mr Blair said. ''If people wreck the assembly, then the rest of it will be wrecked too.''

However, following the latest poll, conducted for the Belfast Telegraph and Ulster Television, with one quarter of the 1,175,000 voters still undecided, there is still a difficult task ahead to persuade reluctant Unionists to back the agreement in big enough numbers.

The extent of the political concern about the burgeoning No campaign was illustrated by the leader of the Liberal Democrats, Mr Paddy Ashdown, on a whistle-stop tour of the province.

Mr Ashdown, who served as a Marine on the streets of Northern Ireland, spoke to Army and RUC officers to hear their concerns about voting for the peace accord and the implications a Yes vote would have for the security services.

After a visit to Ardmore RUC

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station in Newry, County Armagh, Mr Ashdown told The Herald: ''I have been speaking in particular to the security forces because these are the people who have borne the brunt of this, and I think they need to hear some words of reassurance about what is coming.

''My view is very clear. We have

a choice between hope and despair and a Yes vote is just about all the hope there is.''

Mr Ashdown went on: ''In Britain and elsewhere in the world people are longing and waiting to help Northern Ireland back to prosperity and peace but if all they hear on Saturday morning is once again the shout of Ian Paisley and that famous Ulster word 'no' then I think there is a real risk some of those who support Northern Ireland will turn away.''

Meanwhile, dissident Unionists campaigning for a No vote to the peace agreement moved yesterday to try to heal a rift with party leader David Trimble.

They said they would be prepared to back Mr Trimble in a new Northern Ireland assembly, provided it was party policy not to sit down with representatives of paramilitary organisations before all illegal weapons were handed over.

Mr Jeffrey Donaldson, one of six out of 10 Ulster Unionist MPs who have rejected the deal, has resisted a series of attempts by Mr Blair to persuade him to sign up to the accord.

His refusal to back the agreement has heightened the pressure on Mr Trimble to help deliver a 70% majority which the British and Irish Governments would prefer in advance of next month's elections to the new administration.

Friday's referendum is expected to bring the highest turnout of voters yet in Northern Ireland, with 90%-plus predicted in the west of the province.

Mr Donaldson said there was no requirement on the part of paramilitaries to disarm before they enjoyed the benefits of the agreement but confidence-building was a two-way process.

However, he added: ''If the party's policy is clearly one of not sharing in government with those who continue to hold on to terrorism, then that is a policy around which this party can unite.''

Mr Donaldson said people were particularly concerned about prisoner release and the possibility of terrorist representatives becoming ministers in the new government.

Former Tory Northern Ireland Secretary Lord Mayhew said the whole process had been hard for Mr Trimble, who had shown courage.

''It would be an immense pity and not far short of a disaster if that courage wasn't rewarded by a substantial Unionist Yes vote,'' he told BBC Radio Four. ''Unionists should lift their eyes a bit and look at the bigger picture.''