So Mandy's brought up the idea of a public debate between Brown and Cameron again, claiming – in interview with Sky (see footage above) – that the PM would "relish" the opportunity to "take the fight to the Conservatives". If you remember, the last time Mandy mentioned it, Downing St quickly moved to dampen all the speculation - the rumour was that Brown was going to challenge* Cameron to a series of debates in his conference speech, and was irritated at the PoD for giving the game away so early. But now that Mandy has made the same point again – indeed, even more forcefully this time – I reckon it near confirms that Brown's challenge will come soon enough.
* The word "challenge" is used in the loosest possible sense here. After all, it's Cameron who's been calling for these televised debates for some time now.
P.S. In the same interview, Mandelson also said that he has “no prospect and no plans of standing as leader of the Labour party," adding that his peerage is “for life”. See footage here.