To prevent what could be damaging information from being revealed, the White House invoked what is known as "executive privilege" to stop staff testifying.

Executive privilege is a defence used by presidents to stop investigators from prying into conversations held inside the White House. It is based on the premise that private discussions between the president and his White House staff are subject to the same kind of legal protection as discussions between an attorney and their client.

In May, a federal judge rejected Mr Clinton's claim that his conversations with aides about the Monica Lewinsky investigation were not protected under executive privilege. When Kenneth Starr petitioned the court for a quick judgement, the White House withdrew its case, aiming to prevent a quick resolution and judgement by the court.

Dangers of history

What is so dangerous about the use of executive privilege - and a key reason why Clinton avoided going all the way to the Supreme Court to defend it - are the overtones of the Watergate scandal and downfall of President Nixon.

The notion of Executive Privilege was defined in a 1974 Supreme Court ruling, United States v. Nixon which said that private conversations were protected but the Court also rejected President Nixon's claim of an absolute privilege (such as attorney-client) that completely shielded disclosure of all internal communications.

The Court argued that unless there was the need to protect military, diplomatic or national security secrets, the president's general interest in confidentiality could be outweighed by the clear and demonstrated need for evidence in a criminal proceeding.

Defeat in the showdown meant that Nixon had to turn over the tapes of conversations in the Oval Office and only 17 days after the unanimous ruling he resigned.

Clinton's change of tack was no doubt partly guided by the desire not to be the first president since Nixon to take an executive privilege claim to the Supreme Court, a case he would probably have lost.