UPDATE :
Nick Robinson (who broke the story), re-confirms that Boris is considering running. Boris has put out a statement “Being Mayor of London would be a fantastic job and anyone who loves London would want to consider the possibility very carefully. I want to stress that this idea did not come from David Cameron or from anyone in his office but I have, of course, been very struck by the number of people who have been urging me to run. In my case, there are huge obstacles – above all my commitment and responsibility to my constituency. It is hard to see how those difficulties could be overcome – but I am ruling nothing out.”