Unfortunately in this instance there are very good reasons to suspect geographically significant differences in interpretation. It's a known fact, for instance, that white people are more likely to list their religion as 'Christian' if they live in or right next to a large concentration of minorities.
In London, perhaps (complicated by African/Carribean community presence). Though there is a striking difference in South London and again in the more 'trendy' parts of North London that are cheek by jowl next to non-Christian religious areas
I think there is a regional pattern here. Wales isn't shown (but was asked the same question) and there's a high wall of Nones at the border. Urban West Midlands is more 'pink' than urban West Yorkshire. Indeed outside the Severn/Wash line the map is almost topographic with deeper red hues in upland areas.