Sinn FΘin insists that its acceptance of office facilities at Westminster will not herald the beginning of the end of the party's policy of abstention from the British Parliament.
And a party spokesman told The Irish Times that this would remain the position even if the oath of allegiance to Queen Elizabeth was dropped as a requirement for elected MPs wishing to take their seats.
At the same time, the party's president, Mr Gerry Adams, claimed the experience of the Police Ombudsman in her investigation of the RUC's handling of the Omagh bombing had "vindicated" Sinn FΘin's refusal to endorse the new policing dispensation in Northern Ireland.
And he warned the Prime Minister, Mr Tony Blair, of his determination to have "an ongoing engagement" over the murder of Mr Pat Finucane and other allegations of collusion between the security forces and loyalist paramilitaries.
MPs will be asked on Tuesday to reverse the ruling of the previous Commons Speaker, Ms Betty Boothroyd, and permit Sinn FΘin MPs to enjoy office and other facilities at Westminster without being required to swear the oath and take their seats in the Commons chamber. A Sinn FΘin spokesman last night confirmed his understanding that the party's four MPs would be entitled to draw on various parliamentary allowances for research and secretarial assistance and possibly for London living costs, but that they would not be paid their parliamentary salaries.
Insisting "there is no possibility of the policy of abstentionism toward the British parliament changing", the spokesman said the decision to grant office facilities was overdue and would result in "an even more vigorous Sinn FΘin profile in London" than before.
The Democratic Unionist MP for North Belfast, Mr Nigel Dodds, condemned what he called "the secret deal being hatched behind closed doors between IRA/Sinn FΘin and the (British) government".
However, the move did not appear to trouble the First Minister, Mr David Trimble, and was warmly welcomed by the Deputy First Minister, Mr Mark Durkan, as representing "another part of Sinn FΘin's immersion into the constitutional fabric."
Speaking after their joint meeting with Mr Blair at Downing Street, Mr Trimble anticipated "a lively discussion" when the issue was debated next week and said it would be interesting to see "how republicans explain this as a huge step towards a united Ireland" when they "seem to be moving in a different direction."
Mr Durkan said: "The significant thing is that there may have been a change of attitude on the part of the Commons authority."
But he added: "The really significant thing is Sinn FΘin have been insisting on getting into Westminster and attach such great importance to it."
The Prime Minister's official spokesman said the move meant parliament could play its part in advancing the peace process further.
Mr Trimble and Mr Durkan held "useful" discussions on a range of Executive and political issues with Mr Blair during their first formal joint meeting with the Prime Minister since their election as First and Deputy First Ministers.
During his separate meeting with Mr Blair, Mr Adams repeated his view that policing arrangements for Northern Ireland had to be "brought back to the terms of the Good Friday agreement."