Sinn Fein leader Gerry Adams will have to apply to the Treasury in order to resign as MP for Belfast West.
The Speaker's office told ePolitix.com that despite the fact that Adams has never taken his seat in the Commons, the procedure by which a member forfeits their seat must be followed.
In 1624 the Commons passed a resolution banning MPs from resigning their seats.
It states simply "that a man, after he is duly chosen, cannot relinquish".
To this day death, expulsion or disqualification are the only ways out.
Under the Act of Settlement, any Member of Parliament accepting an office of profit under the Crown must give up his or her seat.
So an MP who wants to resign from the Commons applies to the chancellor for one of two offices that exist just for this purpose: Crown Steward and Bailiff of the three Chiltern Hundreds of Stoke, Desborough and Burnham, and Steward of the Manor of Northstead.
They were retained as nominal offices of profit solely to meet the requirements of the House of Commons Disqualification Act 1975.
Adams is resigning so he can stand for election to the Dail, the Irish parliament.
A spokesman for Mr Speaker said that while it is usual for a member of a former MP's party to move the writ for a by-election, it can actually be moved by any member of the House.
It is likely that a government whip will move the writ.
Dods Parliamentary Communications Ltd