All the opinion polls
show that neither Boris nor Ken have much chance of winning the London Mayoralty on purely first preference votes so the race is going to be determined by second preference votes from people whose candidate failed to make the run-off. The largest of these groups will be Lib Dem supporters. No one is quite sure which way they will jump but if Boris was to announce that his second preference, which will be meaningless as he will be one of the top two candidates, will be for Paddick he might lure some of them over to his side.
It would also send the message that he is a Liberal Conservative which is particularly important given the nature of the London electorate. Boris needs to deal with the fact that some on the left are trying to smear him with the fact that he will receive some second preferences voters from BNP supporters, support that Boris has repeatedly—and rightly—said that he doesn’t want.
PS Further endorsements for Boris in the papers today with The Times and The Daily Mail both coming out for him.