The Government will now confirm the go-ahead for the March 7 election with the current 'transitional' Assembly coming to an end at midnight tonight. The Irish and British Prime Ministers are expected to meet tomorrow.

After a seven-hour debate at the Royal Dublin Society, Sinn Fein delegates overwhelmingly reversed 100 years of opposition to police and court structures. On a card vote, more than 80% who voted backed the party leadership's move.

The decision has been welcomed by Prime Ministers Tony Blair and Bertie Ahern, Chief Constable Sir Hugh Orde and the Secretary of State Peter Hain. DUP leader Ian Paisley said his party had forced Sinn Fein to support the PSNI.

Only a few dozen of the 1,000 delegates voted against, and some others appeared to have abstained.

But the carefully crafted motion now leaves implementation of the new policing policy up to the party's ard chomhairle (executive).

And it was made clear implementation will depend on the restoration of power-sharing devolution, even it that does not happen by the St Andrews blueprint deadline of March 26.

Gerry Adams said the ard fheis had acted "in the national interest" and it was now up to others to do the same.

After the result, he told wildly cheering delegates: "Today you have created the potential to change the political landscape of this island forever."

The Sinn Fein president said it was a "truly historic" decision, but its significance would be in how the motion is used "to move the struggle forward - to Irish unity and the British Government leaving Ireland" .

And he appealed to unionist leaders to "take up the challenge" of real, "anti-sectarian" dialogue with republicans - but insisted " there's no going back".

The party's chief negotiator, Martin McGuinness, said yesterday was a " big day" for Sinn Fein, but today is an even bigger day for DUP leader Ian Paisley.

He said the result which the DUP and others wanted from the ard fheis was their "favourite word" - a "resounding no".

For some former comrades, Sinn Fein's decision was a step too far.

Ex-IRA prisoner Gerry McGeough, a member of the Provisionals' East Tyrone Brigade during the Troubles, was among those who criticised the vote to endorse the police.

"I am not surprised by the result," he said.

"This was a classic, textbook case of counter-insurgency. The British have succeeded in imposing their policy of divide and rule.

"A significant section of the republican movement has been recruited into the British Crown system and is being used to administer and maintain British rule in Ireland for a very long time."

The president of the dissident Republican Sinn Fein, Ruairi O'Bradaigh, said: "The British will seek to have them complete the work of collaboration by steeping their hands in the blood of Irish republican activists.

"That is the lesson of history which has been borne out step by step since 1986. Ultimately, the Provos will be indistinguishable from the unionists in their support for British rule in Ireland."