The Prime Minister's wife Cherie Blair asked for a media blackout last night when she addressed students at the Oxford Union.

Mrs Blair, whose professional name is Cherie Booth, was due to speak in her capacity as a human rights QC for the legal firm Matrix Chambers.

But according to the Oxford Union president Theo Roos, Mrs Blair decided to be coy about journalists wishing to attend the event.

He said: "It would be great for the Oxford Union to be able to open this to the press and great publicity for us.

"The only problem we have is that she would not speak if there were press there. She only wants Oxford Union members."