Using data from the 2011 UK census, Oliver O’Brien at University College London’s Centre for Advanced Spatial Analysis created a tool called DataShine so you could see all sorts of information, including which cities had the highest rates of people claiming “No Religion” (in dark blue):

You can see a summary of the results here. When I visited the DataShine website, it was running very slowly for me, but hopefully it’s faster by the time you check it out.
(via The Guardian — Thanks to Brian for the link)