Eastbourne MP Nigel Waterson yesterday failed in an emotional plea to stop Parliament giving Sinn Fein members office space.
Mr Waterson asked how he could be expected to explain the decision to his constituents, who saw one of their former MPs murdered by the IRA.
Ian Gow, a former Parliamentary aide to Margaret Thatcher, was blown up by the IRA before its declaration of a ceasefire.
Mr Waterson questioned how the Commons could think about giving benefits, privileges and facilities at Westminster to "some of the people responsible for his murder".
Leader of the Commons Robin Cook agreed Mr Gow was "tragically and appallingly murdered".
But he added it was important to the peace process to engage Sinn Fein in political activity.
Mr Cook said: "The whole point of the peace process is to prevent future murders of that kind and to ensure that we proceed, by political activity, not by violent confrontation."
After an emotionally-charged Commons debate, MPs backed the Government plans for the controversial move by a margin of 322 votes to 189.
Sinn Fein's MPs have consistently refused to swear the oath of allegiance to the Queen, which has left them barred from the parliamentary privileges afforded to other MPs.
The change means the four Sinn Fein MPs - Gerry Adams, Martin McGuinness, Pat Doherty and Michelle Gildernew - can enter the Commons precincts when Parliament returns in the New Year.
As well as using support services, the MPs can each claim £107,000 a year in allowances to cover staff salaries and expenses.
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