AnFI
If there is widespread FZFG, low cloud, poor visibility, temperatures around -5 & -6 and nil spread - how can you can you be so adamant in dismissing icing?
Even if you can fly in clear dry air (it was over London in nil wind so I seriously doubt it was crystal blue!), you still have to land. And you will be flying in cold air in a cold aircraft. So unless you are flying above an inversion - the incipient icing conditions below would almost certainly accumulate on the aircraft once you descend back into the saturated air below. And the ice might like your aircraft anyway, even if it is initially warmer than the icing conditions.
Seriouly AnFI - what do think is causing visibility to be poor, if not ice-cold condensation?