A senior White House aide at the centre of a CIA leak investigation learnt the identity of an undercover agent from his boss, Dick Cheney, it was claimed today.

Lewis "Scooter" Libby, the Vice-President's chief of staff, gave evidence to a grand jury that he first heard the name of covert agent Valerie Wilson, nee Plame, from journalists at around the time that her name was printed in a newspaper column.

But according to The New York Times today, lawyers involved in the case say that notes in Mr Libby's own handwriting show that in fact he first heard of Mrs Wilson from Mr Cheney.

Patrick Fitzgerald, a special prosecutor who is leading the investigation, has heard allegations that Mrs Wilson's name was leaked to the press by the White House as revenge against her husband, a retired diplomat, for a scathing article he wrote about the lack of evidence for weapons of mass destruction in Iraq.

There is nothing illegal in Mr Cheney and his chief of staff, discussing a CIA agent. Publicising the name of a covert CIA agent is a criminal offence only if the person who reveals it knows that that the spy is an undercover agent.

Lawyers close to the case, who described the notes to The New York Times, say that there is nothing to show that either Mr Cheney or Mr Libby knew that she was an undercover agent or that her identity was classified.

But the appearance of the Vice President's name in the leak inquiry is likely to increase the pressure on the Bush Administration, which is trailing in the opinion polls.

The role of both Mr Libby and of Karl Rove, President Bush's senior policy adviser, in possibly revealing Mrs Wilson's name during conversations with journalists has come under scrutiny.

The notes suggest that it was George Tenet, the head of the CIA, who told Mr Cheney about Mrs Wilson. Her name appears to have cropped up because of her alleged role in sending her husband to Niger on a mission to investigate White House claims that Saddam Hussein tried to buy raw uranium for a nuclear weapons programme.

Mr Wilson concluded that there was no evidence, and annoyed the White House by writing a newspaper article saying so.

Both Mr Tenet and Mr Cheney gave evidence privately on oath to the special prosecutor last year, and have not appeared before the grand jury.

Mr Libby's notes have been given to Mr Fitzgerald as part of his inquiry. He is expected to decide by Friday, the day that the grand jury's remit expires, whether to bring charges against anyone in the White House.

The White House has refused to comment, as has Mr Libby's lawyer, according to The New York Times.

Mr Libby and Mr Rove attended a Cabinet meeting with President Bush yesterday, as the White House sought to portray the impression of business as usual. It is likely however that any aide who is indicted by Mr Fitzgerald will have to quit their job.

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