The British and Irish governments hope the announcement, now believed to be imminent, will be strong and unambiguous enough to inject a burst of new momentum into the stalled peace process.
The thrust of the announcement has been thrashed out in intensive contacts between Tony Blair and his officials and Sinn Fein leaders Gerry Adams and Martin McGuinness. The central point is that the IRA will declare an end to illegal actions such as recruiting, training and surveillance, as well as promising an end to activities such as bank robberies and similar criminality.
The IRA is expected to say it is putting its entire weapons cache beyond use in weeks. That will be verified by the decommissioning expert General John de Chastelain, who has already witnessed three partial acts of decommissioning. Although he acted alone before, this time he is expected to have a Catholic priest and a Protestant minister as other witnesses.
The Government is poised to react with a battery of security relaxations that will include the demolition of military watchtowers along the border, and an agreement to permit "on the run" republicans to return to Northern Ireland. The hope is that the IRA moves will impress the Rev Ian Paisley, whose Democratic Unionist party is now the undisputed leader of Unionist politics. He alone can pave the way for a new devolved government dominated by his party and Sinn Fein.
But he is not expected to agree to that immediately and is, instead, expected to watch for some months to verify that illegal IRA activity has ceased. The authorities will ask the International Monitoring Commission to confirm that the IRA has gone out of operation.