Elizabeth Filkin: "Complaints can be laid at my office"

Miss Filkin told BBC Radio's The World At One it was up to the Committee on Standards in Public Life, which is chaired by Lord Neill, to decide the arrangements on how MPs and ministers are governed.

But Miss Filkin, who takes up the post in February, agreed her office was set up to carry out investigations and it could do so.

Her predecessor Sir Gordon Downey has previously pointed out that there was a gap in the system of parliamentary scrutiny.

"It may be that it would be a better arrangement to have investigations when they are needed to cover both MPs in relation to the House of Commons and, indeed, what they do if they happen to be in ministerial positions," said Miss Filkin.

Peter Mandelson: Did not declare flights

Complaints against MPs, made by their colleagues or by newspapers, could be laid at her door, said Miss Filkin.

She would also be looking closely at the register of members' interests, Miss Filkin went on.

She said: "I do have the duty, when I take up my job, to monitor the register of members' interests.

"Obviously when I take up my job, I will be looking to see what that monitoring consists of."

Shadow Trade Secretary John Redwood has written to Miss Filkin, urging her to widen her inquiries to include the fact former trade secretary Peter Mandelson failed to declare "at least one free flight" in the private jet of American millionaire Linda Wachner.

Mr Mandelson resigned last Wednesday after it was revealed that he had borrowed £373,000 from former paymaster general Geoffrey Robinson, who also resigned on the same day.

Mr Mandelson confirmed he accepted a free flight on Ms Wachner's private jet and failed to declare it to Parliament. But he said the flight was based on friendship and was not linked to his job as an MP or minister.