Similar trends have been observed in Britain and in other European countries with substantial Catholic and Protestant populations.
There's a link to religious minorities in general; in England most of the highest rates of Christians in the last census were in areas with big Catholic populations, with a strong Nonconformist tradition or both (hello Wigan!). Another interesting thing is that if you look at the data at a lower level, people are apparently more likely to identify themselves as Christians if they live in or near an area with a big population of people from a non-Christian religion. Another interesting trend; traditional, "stable" working class areas and the better-built (originally) estates ended (almost everywhere) to have lower rates of people claiming No Religion than system-built estates built, initially, with relatively few amenities.
