Peter Mandelson - why was he so keen to "get" George Osborne

Further to my earlier post, Tim Walker, Telegraph's Mandrake reminds us that:

"Before Nat's letter was published, I had been informed that the Opposition planned to ask ministers about a taped conversation possessed by the FBI, which explains why Deripaksa's entry visa to America was revoked. As I revealed in The Sunday Telegraph at the weekend, it was said to be an "explosive" telephone call."

Hmmm...