If a constituent believes that they have been unfairly treated by a government department then they can complain to their MP who may pass the complaint to the ombudsman.
The function of the ombudsman, officially called the Parliamentary Commissioner for Administration, is to investigate these complaints and to report the findings to the department involved and the constituent's MP.
If the ombudsman finds that the constituent has been treated unfairly he will request that the department involved corrects their mistake, either with an apology or compensation. In the vast majority of cases the advice of the ombudsman is followed.
The ombudsman publishes an annual report to Parliament and his work is reviewed by the Select Committee on the Parliamentary Commissioner for Administration.
There are separate ombudsmen for the National Health Service, Northern Ireland and Local Government.
The office was established in the 1960s and the name derives from a similar position in the Scandinavian countries.