Guido Fawkes says that Brooks, who was re-arrested and bailed earlier this month in the police probe into newspaper phone hacking and corruption, has been informed of her "impending star turn" at the inquiry.
The blogger said that Brooks was asked yesterday to take the stand at the beginning of May. But there has been no confirmation on this from the Leveson Inquiry, or other sources.
The inquiry was set up by David Cameron to investigate press ethics and standards in the wake of the hacking affair that engulfed the News of the World.
The Sunday tabloid was published by a subsidiary of News International until it was axed last July after a string of shocking revelations, including that journalists had intercepted the voicemails of murdered schoolgirl Milly Dowler in 2002.
It is expected that Brooks will be limited in her evidence due to ongoing police investigations, but her appearance will provide some awkward moments for the prime minister.
Cameron is a close friend of Brooks's racehorse trainer husband Charlie as they were at Eton together. It also recently emerged that the prime minister rode a horse loaned to Brooks by the Metropolitan Police.
Fawkes was summoned to Leveson himself last year to explain how parts of the witness statement of Alastair Campbell, the former spin doctor to Tony Blair, had leaked out early.
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