Members of the proposed Northern Ireland Assembly will also be able to serve as members of the Seanad, The Irish Times has learned.
MPs at Westminster will tonight approve the Northern Ireland Elections Bill paving the way for Assembly elections on June 25th, subject to a Yes vote approving the Good Friday agreement of May 22nd.
Sources last night confirmed that the British legislation does not contain a clause which was used to bar Mr Seamus Mallon, deputy leader of the SDLP, from the 1982 Assembly on grounds of his membership of the Seanad at that time.
On Sunday Mr Martin McGuinness told the Sinn Fein ardfheis that, in the final hours before the Good Friday agreement was concluded, the party had separate negotiations with the Irish Government "on the question of prisoners in their jurisdiction, on constitutional matters, and the rights of citizens in the North to be represented in Irish political institutions in the South".
Mr Gerry Adams, the Sinn Fein president, had previously argued that he should be permitted as the elected MP for West Belfast to represent his constituents in the Dail. But it is understood the British legislation extends only to the Seanad, with sources drawing an analogy with the ability of people like Lord Alderdice, the Alliance leader, to sit in the Assembly while retaining his membership of the House of Lords.
MPs face a nine-hour session to complete the legislation for the Referendum and Assembly elections, and the order bringing the Northern Ireland Forum to a close. And British ministers are bracing themselves for a possible unionist assault on the key issue of decommissioning paramilitary weapons.
Mr David Trimble, the Ulster Unionist Party leader, is leaving today for a four-day trip to the US, and it was unclear last night whether in the absence of Mr John Taylor and Mr Ken Maginnis the UUP case in the Commons would be put by Mr Jeffrey Donaldson, who has opposed the agreement.
The possibility presents itself as a first practical indication of the difficulties Mr Trimble could face at the Westminster level, given that a majority of his MPs have refused to support him on the agreement.
Mr Donaldson has previously indicated his intention of seeking to amend the elections legislation in order to stipulate that prior decommissioning of IRA weapons should be a condition of Sinn Fein entering the proposed Northern Ireland Executive. But it is clear that any such amendments moved tonight will be voted down by the government.
If, as expected, the elections Bill completes its stages in the Commons today it will proceed to the Lords on May 7th so that the legislation will be on the statute book in time for the planned June 25th elections. The Bill makes clear that the elections to the 108-member Assembly are dependent on a Yes vote in the referendums North and South on May 22nd.