Downing Street says that the call for Lord Irvine's resignation should be treated "with the contempt it deserves."

The call came from the Conservatives, who claim that the Lord Chancellor has damaged the integrity of his office, by writing to Labour lawyers appealing for contributions to the party's campaign fund.

The Tory argument that goes that the lawyers - all of whom had dinner with Lord Irvine - might feel under undue pressure, because he is responsible for all major legal appointments.

Michael Ancram, the Tory chairman, added that he wants to know which of the lawyers responded to Lord Irvine's appeal, and how much they gave.

Asked why the resignation-call had been delayed so long, Mr Ancram explained that they had wanted to wait for a formal Government response before taking the matter further.

Labour argue that Lord Irvine has done nothing wrong. He was acting as any senior member of the Labour Party might do in appealing for funds.

Ministers say there are no plans to change the rules governing the Lord Chancellor's position.

Triple role

But the case has exposed once again the underlying constitutional issue - the number of hats the Lord Chancellor wears.

He is, at one and the same time, head of the judiciary, a senior member of the legislature (the speaker of the House of Lords) and a member of the executive - Tony Blair's cabinet. In most countries, these powers are separated in the constitution.

Until 1992, it was Labour policy to split the roles. Some within the party believe the policy should be revived.

Geoffrey Bindman, the chairman of the society of Labour lawyers, attended the Irvine dinner and dismisses out of hand the idea that any of his members might have felt intimidated.

But he does believe the time has come for the Lord Chancellor's multiple roles should to be reviewed.

He was sympathetic to the idea of a Justice Department with a minister sitting in the Commons.

And his views were supported by Diana Woodhouse, Professor of Constitutional Law at Oxford Brookes University.

She said that Lord Irvine was much more active in party politics than most of his predecessors. This could give rise to the perception of a conflict of interest.