The former Prime Minister said the change would be constitutionally wrong and "a step too far". Tory MPs also protested to the Speaker, Betty Boothroyd, in the Commons.
She told MPs that ministers had approached her to allow the Sinn Fein president and his negotiator, Mr McGuinness, to have access to the Palace of Westminster. "Should ministers now wish the two Sinn Fein members to have access to some of our facilities it would be for the Government to put a motion to that effect," she said.
Mr Major accused the Government of bypassing Parliament and said that the Conservative Party had not been consulted about the important constitutional change that would be involved.
The Prime Minister insisted he had "no plans to introduce alternative versions of the oath of allegiance".
Downing Street said Mr Blair had talks with the Speaker over the two Sinn Fein MPs, who won Westminster seats in 1997 but did not take them up. A spokesman said MPs wanting to sit in the Commons would still be required to take the oath. The talks were over using Commons rooms, without seeking to speak in the chamber.
Ministers believe the appointment of the two Sinn Fein chiefs to the Northern Ireland power-sharing executive has made the bar on their visiting the Commons ridiculous.
The issue was raised as the Government published a Bill that will enable members of Sinn Fein to stand for the Dail, the Irish parliament, in spite of holding seats in the Assembly and the Commons. The Bill is intended to cement Sinn Fein into the peace process, offering it the chance to gain a hold on power in Dublin as well as Belfast. The Bill will not allow members to hold ministerial office in more than one assembly or parliament.
Both Mr Adams and Downing Street denied the move was linked to the decommissioning of weapons by the IRA. Mr Adams told BBC Radio Ulster the cross-border development was "a considerable success" for Sinn Fein, which recently lobbied an Irish Parliament committee for representation from Northern Ireland. "The breakthrough is in getting a situation where northern [Irish] representatives can take seats in southern institutions and now it's over to the Oireachtas committee to come in with [what] I would think would be positive and progressive findings that would allow that to happen."Reuse content