BBC Legal Affairs Correspondent Joshua Rozenberg reports

The inquiry, which will be held in public, was ordered after a senior official refused for the first time to authorise payments to four leading QCs.

The four include left-wing barrister Michael Mansfield, Christopher Sallon, Peter Feinberg and Richard Henriques.

They are each receiving anything up to half a million pounds for a year's work.

Payments refused

The clerk to the parliaments, Michael Davies, refused to sanction payments because he felt their fees were too high, although in three cases the original sums had already been cut.

The four lawyers have instructed a fellow QC, James Munby, to defend the fees they claimed for appeals that went to the Lords last year.

Michael Mansfield QC has made his name in high-profile cases

The inquiry will consider for the first time whether barristers' legal aid fees should be linked to the going rate for private work, or be based on an income for a highly qualified public service professional.

The Bar Council has instructed leading advocate Sydney Kentridge to represent the legal profession's interests in the inquiry, which will be held before five Law Lords on June 17 and 18.

The outcome could mean a large drop in criminal QCs' earnings - estimated at £300,000 a year or more.

Mr Henriques led the league table of QCs' earnings from legal aid in 1995-96, with more than £500,000, though he said this related to more than one year.

Mr Feinberg featured in the 1996-97 top 20 with earnings between £350,000 and £399,000.

Top earners

Mr Sallon is a former chairman of the Bar Council's public affairs committee. Mr Mansfield, who is currently representing the family of murdered teenager Stephen Lawrence, is famous for high-profile miscarriage of justice cases.

The inquiry has been called for by the House of Lords

At the moment, top QCs earn more than any other profession paid from the public purse, including the judges who hear their cases.

The inquiry could see their earnings reduced to a maximum of about £175,000.

The Law Society is understood to be preparing written submissions to the inquiry supporting the move.

A spokeswoman for the Bar Council said: "I can confirm that there is a case pending in the House of Lords and that in advance of it we can't comment on the details because the matter is sub judice."