Brown calls Peter Watt a liar?

Gordon Brown has been asked in Parliament about the now infamous "fund with no name" that Peter Watt referenced in his book "Inside Out". Asked by David Evenett why it was not declared on the Register of Members' Interest. Brown's response was,

I know nothing about what he is talking about

Apart from the roars of laughter in the Commons, presumably he's either claiming that he hasn't read the newspapers, or noticed a complaint about him to the Parliamentary Standard Commissioner, or, he's calling Peter Watt a liar - having already branded him a criminal and screwing him over as detailed in the book.

Update: Corrected Brown quote after second listening, changed "of" to "about".

UPDATE II: ConservativeHome have a copy of a letter written by Eric Pickles to Gordon Brown suggesting he has misled the House with his response.