Comparing MP's benefits with the rest of the public sector is pointless.
Firstly, let me say I don't agree with what the MP's get in their pension packages but them being wrong does not automatically exempt the rest of the civil service from being sorted out.
We have the option every four or five years to dump MP's (currently with an unacceptable severance package) but we don't get the same situation with the rest of the public sector. If we could vote on whether to sack or keep teachers, police, etc every four years, then maybe a comparison would be apt. Failing teachers would be dumped, fat policemen who could not run after suspects could be let go and anyone who failed to perform could find them on the streets and no manner of excuses from the public sector would be excused - the people would choose.
Somehow I doubt four years contracts for public servants would be something they would support.