The speech is due to commence at 1040 GMT.

 56k modems    28k modems

BBC Ireland Correspondent Denis Murray: The prime minister is acutely aware of the historic nature of the visit

Mr Blair will be the first UK prime minister to address both houses of the Dail since Dublin declared independence in 1922.

He plans to say: "We must not be prisoners of our history. We must put the past behind us.

Public frustrated at lack of progress

"Down through the centuries, Ireland and Britain have inflicted too much pain on one another."

The prime minister's official spokesman said he would go on to make a plea for mutual understanding.

"Just as we must understand your yearning for a united Ireland, so too must you understand what the best of unionism is about," he will say.

"Now the UK and Ireland are two modern countries. We must try to put our histories behind us, and try to forgive and forget these age-old enmities, and look to a better future."

Mr Blair has also offered hope of Ireland re-joining the Commonwealth.

He said the Commonwealth would be a topic for discussion when he meets Ireland's Taoiseach, Bertie Ahern, later on Thursday.

Ireland left the Commonwealth after declaring independence but Mr Ahern says members of his Fianna Fail party have already raised the possibility of rejoining.

Such a move is likely to be welcomed by unionists but may spark suspicion among nationalists.

Historic occasion

Mr Blair will become the first British politician to be afforded the honour of addressing the Irish parliament since 1922 and will follow a long line of heads of state, including John F Kennedy and Nelson Mandela.

His speech comes at what has been described as a "crisis" point for the Northern Ireland peace process.

BBC Ireland Correspondent Denis Murray: "Unique high-point in Anglo-Irish relations"

The UK prime minister, speaking after a day of talks with all parties at Stormont on Wednesday, said he remained confident cross-border bodies and a shadow executive would be up and running in time for the handover of power in February 1999.

"I hope that over the next few days some proper signs of that progress will be shown," Mr Blair said.

Deadlock over decommissioning remains

Optimism was also voiced, although cautiously, by David Trimble, the Northern Ireland First Minister.

But there was an apparent rift between Mr Trimble and his Deputy First Minister Seamus Mallon, who continued to warn that the peace agreement was in danger of unravelling.

Sinn Fein President Gerry Adams also accused unionists of holding up progress with "childish antics" and blatant stalling tactics.

"People are reluctant to use the word crisis, but clearly if this drift is allowed to continue and if the only institution to arise is a shadow assembly at Stormont with two ministers, then the position just becomes untenable.