Right, but as a speaker I thought his seat is uncontested at election time. As you say, it's been a while since one has been forced out, but it is not unreasonable to expect that they resign as an MP under these circumstances, given that they have not had to properly stand for re-election as an MP.
From the BBC - BBC NEWS | Politics | Speaker announces he is to quit
Speaker announces he is to quit
Michael Martin has told MPs he intends to stand down as Commons Speaker, amid criticism of his role in the MPs' expenses row. He told MPs he would relinquish the office of Speaker on 21 June -...
My understanding was that he was overly harsh towards those MPs who questioned MPs expenses in the House, plus allowing the police in to arrest that MP a while back didn't do him any favours, by all accounts.