The tribunal in south London found in favour of immigration lawyer Jane Coker who argued that Lord Irvine's appointment of Garry Hart was unlawful as the post had not been advertised.

Garry Hart: Long-time friend

But the panel cleared him of direct discrimination - the deliberate choice of one person over another on the grounds of sex or race.

It also rejected allegations of racial and sexual discrimination brought by another female lawyer, Martha Osamor.

Lawyers for the lord chancellor had argued that the appointment of special advisers was exempted from civil service regulations and he was not required to advertise the post.

Lord Irvine himself did not attend the tribunal saying it would only add to the publicity surrounding a case he claimed had no merit.

After the hearing, Ms Coker called for a change in the way the government appoints staff.

"Our case has shown that this government's procedures for appointing special advisers discriminate unlawfully against women and black people," she said.

"There are 69 special advisers to this government. This decision goes to the heart of central government. It must change now to begin to comply with its stated commitment to equal opportunities."

Call for Lord Irvine to quit

She and her fellow lawyer Ms Osamor said the Lord Irvine should resign because he had broken the law.

And their solicitor Jane Deighton added to their calls for him to go. "The disdain with which he treated women and black people is matched only by the arrogance with which he has treated the law and these proceedings.

"He's the head of the legal system. This decision means he has to resign," she said.

Blair's role

The complainants had tried to implicate the prime minister himself on the grounds that Lord Irvine had discussed the appointment with him.

However, the tribunal ruled it was too late to name Tony Blair as a respondent in the case.

The Lord Chancellor's Department said it would be considering an appeal against the ruling.

Earlier this month the lord chancellor provoked controversy after he admitted using government stationery to invite friends to a private funciton at London's Garrick Club.