It's all a question of language...
Lord Brown: "I have never placed a bet at all while a minister ever on a political issue".
The crucial words here are "at all while a minister". Why put that in Lord West? Why throw that in?
The bet was made after Brown became Prime Minister - 28 June 2007
Lord West became a minister - 1 August 2007.
That leaves a 34 day gap where Brown was bouncing, the odds were high and Lord Brown was not a minister...
You say "I have never placed a bet on Labour losing the election" but can you confirm if you placed a bet that the Conservatives would win one, or that Labour would win in coalition? You do not rule out placing a bet, you just rule out that specific bet.
It's all about the language of the bet placed and the language West is using. Somehow, I think Lord West has been caught out. Somehow, I think Lord West placed a bet at 66-1 between 28/6/07 and 01/8/07. What say you, m'lord?