I don't pretend to understand the inner workings of the Lib Dem party machine. It may well be the case that they intend to have two candidates for Mayor of London, one for north London and one for south.
If that is the case then Fiyaz Mughal is pitching for the north London gig. He has even called his website "Is it cos I am a North Londoner?".
Fellow south Londoner Duncan Borrowman sums things up rather well.