Cabinet minister Peter Hain faces further pressure over his failure to declare political donations when he faces questions from fellow MPs in the House of Commons on Wednesday for the first time since the row began.

Questions over the funding affair are likely to be ruled out of order when Hain appears for Welsh questions, but opposition MPs will be keen to use the opportunity to embarrass the Work and Pensions Secretary.

Prime Minister Gordon Brown repeated his support for Hain on Tuesday night, describing the failure to declare more than 100,000 pounds of donations as no more than a mistake and "an incompetence".

Brown told ITV's News at Ten that the matter was now in the hands of the Commons Standards Committee and the Electoral Commission.

"I believe that they will understand that this was a failure but there was no corruption involved, no illegal donation made, and I hope that they will be able to accept his apology," Brown said.

"Peter Hain has confessed to his mistakes and he has apologised in the most profuse terms for what has gone wrong.

"It was a mistake that was made, it was an incompetence that he has readily admitted to."

The office of the Parliamentary Commissioner for Standards is investigating Hain's conduct after a complaint was received from a backbench Conservative MP last week.

The Electoral Commission is conducting its own inquiry into the donations, raised to support Hain's unsuccessful campaign for Labour deputy leader last year.

Hain says poor administration by his campaign team was to blame for the failure to declare the cash, adding that he is happy for inquiries into the donations to take their course.