It looks like Boris Johnson is being found out rather quickly. I don't think keeping him hidden away will fool the London voters. I suspect that David Cameron and the Tory leadership never thought Boris, or BoJo to his friends, would seriously challenge Ken Livingstone.
Now he is in with a chance Cameron has problems. Does he keep Boris quiet and hope to win on an anti-Ken vote, but then face a year or so of extreme embarrassment as Boris is allowed to speak again as London's Mayor? Or does he let him speak and lose London? Maggie lost London and disbanded Ken's GLC so maybe that's his answer.