Outgoing Commons sleaze watchdog Elizabeth Filkin is being asked to give evidence to a committee investigating the system for regulating MPs' interests.

The Committee on Standards in Public Life, chaired by Sir Nigel Wicks, is set to investigate concerns that the system for registering and monitoring MPs' outside interests is in need of an overhaul.

Their investigation was prompted by Filkin's decision not to re-apply for her post, claiming her independence could no longer be guaranteed.

Her move came amid claims that ministers had attempted to undermine her position as parliamentary standards commissioner during investigations into allegations of misconduct.

The standards committee decided in December to review how the system of self-regulation for MPs was working in practice - "taking account of subsequent developments".

Meeting on Thursday, committee members began drawing up a list of potential witnesses, with Filkin heading a list thought to include MPs, journalists and former and present members of the standards and privileges committee to which Filkin reports.

The inquiry is likely to begin in March, with evidence being taken at public hearings and through written submissions.

The committee is also expected to publish a consultation paper looking at the key issues together with a timetable for proceedings next month, before producing its final report shortly before the summer parliamentary recess.

Wicks has already written to Commons speaker Michael Martin - who is the chairman of the House of Commons Commission which is responsible for appointing Filkin's successor. He is seeking clarification on the appointments process for the post, the time commitment and workload, and the question of the tenure available to the holder of the post.

It followed a row over Filkin's decision not to reapply for the post because it had been "downgraded" with fewer hours and a lower salary.

She also said ministers, MPs and their supporters had participated in "whispering campaigns" aimed at undermining her authority as she conducted investigations into allegations of sleaze and improper conduct.

Members of the standards in public life committee are said to be concerned that Filkin had been badly treated by the Commons' authorities, and Wicks has already stated that the committee "is not able to see the justification for reducing the time commitment of the post".

The worries have been rejected by both the Leader of the Commons, Robin Cook, and the speaker.

Martin has said that the Commons Commission only acts in line with the system determined by MPs and is "committed to transparency and openness".

"We have no intention of effecting any change in the role or function of the Commissioner, nor of threatening the impartiality of the holder of the post...We wish to see as the next commissioner for standards someone of standing, ability and personal authority, able to establish credibility both outside and inside the House," Martin said in response to Wicks' concerns.