How to deflect the truth

The following is a question from the new No 10 Mc'A' level qualification that is deemed to have equivalence to a nobel prize and PhD in Physics according to Ed Balls and co:

National No10 communications exam - sample paper:

Person A sends a letter to person B.
Person B ignores the letter and throws it away saying "I'm not bloody answering that or taking any notice of Tories" - as usual. ( Candidates are reminded this is a hypothetical question - and you can't prove otherwise . )

Question:Later a scandal emerges and it turns out that A says they warned B about that scandal. How can B deny it yet stay within the bounds of the truth ?

Model answer:
Downing Street says it has no evidence that the PM received a letter from the Conservative Party warning that an MP's conversations may have been bugged.

But anything that calls into question whether the letter was sent and implies it was never read - without actually saying so - will receive full marks.

Those who attempt the A Campbell gambit of attacking the letter writer and smearing them will receive half marks for effort.

No marks will be awarded for saying "Yeah we got that but as usual Gordon ignores everything Tories say, unless its a policy he needs to steal to stay in power."