The INLA, one of the deadliest and most ruthless paramilitary groups in the Northern conflict, is preparing to disband. The organisation, which has held secret talks with the British, believes the time is right "to leave the stage".

A keynote address outlining the INLA's future is expected to be made this afternoon in Bray at a commemoration for Seamus Costello, the group's founder. The speech is due to be delivered by Martin McMonagle from Derry, a leading member of the INLA's political wing, the Irish Republican Socialist Party (IRSP).

The INLA's intention to disband will be welcomed by the British and Irish governments and Sinn Fein as strengthening the peace process.

While the INLA won't announce decommissioning, it hasn't ruled this out in future. Although it opposes the Belfast Agreement and the Police Service of Northern Ireland, it says current political conditions aren't right for republican paramilitary groups to exist.

It believes disbandment will allow the IRSP to grow. Future negotiations over decommissioning may involve demands for both governments to release INLA prisoners and also for funding for schemes to help ex-prisoners.

Despite the INLA's intentions, the Real IRA and Continuity IRA last night vowed to continue their campaigns. The Real IRA, which murdered two British soldiers at Massereene in March, said it had no intention of calling a ceasefire or disbanding.

"We are strengthening our ranks," a source said. "What the INLA does is its business. Our position is simple – while the British occupy Ireland, Irish people have the right to armed resistance."

The INLA has undergone an intensive internal debate on its future over the past year. It has several hundred members on both sides of the Border. It's strongest in Belfast, Dublin, Derry, Dundalk, Strabane, Galway and Waterford. It believes its membership will not join other republican organisations. Dissident sources predict some defections.

During the late '70s and early '80s, the INLA rivalled the IRA for dominance. In 1979, it killed Airey Neave, Margaret Thatcher's close aide, in a House of Commons car bomb. Three INLA prisoners died in the 1981 hunger-strike. But the INLA was later weakened by internal feuds.

In 1997, the INLA murdered loyalist leader, Billy Wright, in the Maze. The following year, the organisation called a 'no first strike' ceasefire. It didn't target the security forces but retained the right to defend the nationalist community and retaliate were attacked.

Recently, the INLA has murdered several alleged drug-dealers. In March, it stood down its controversial Dublin leader, Declan 'Wacko' Duffy. Formed in 1974, with a mix of hardline republican and Marxist politics, the INLA's best known leader became Dominic McGlinchey who was murdered in 1994.