Will Boris Johnson Stand Again?

There seems to have been a sudden burst of speculation about either Lord Mandelson or Boris Johnson standing as London Mayor in 2012. The Mandelson stuff seems quite plausible to me, certainly more so than David Lammy. Johnson standing again also seems unavoidable for him unless he wants a reputation as a diletante quitter. However, I can't think of any reason why he couldn't win a second term as Mayor, and then serve consecutively as a MP for a Tory seat in London, as French politicians seem to.