I don't think it has declined so much as many people in UK have not been very religious for 50 or 60 years now. But it is now perfectly acceptable to admit the fact.
The one old lady in the UK that I knew that once practiced Christianity now has Buddhist beliefs.
I know only 3 Christians, all of them in Malaysia.
We tend not to inflict an indoctrination on our infants as it seems to be most unfair.
Edit: I am not exaggerating Mark D, it is quite true.
The USA is as Christian as Saudi is Muslim, we just arena`t like that at all. Yeah sure there are lots of Christians in the UK, but I don`t know any.
I've heard people claim that "nobody" they know are theist in UK, but Internet people are known for exaggerating.
Any statistical information I've seen shows that Christianity is still the largest group, and well over 50% in almost all areas of Europe, but some of that information could be several years old. It's probably declined some since some of these statistics, and it's less prevalent there than in the USA, but I don't think it's anywhere near non-existent in any specific European country yet.
Even still, it does seem to be vastly less influential on everyday non-religious things.
I think in both places numbers on paper make Christianity seem like a larger group than is found in the daily practice of people.
For example, in polls like the census or judging by church memberships and such, there seems to be more Christians.
But a lot of people just mark down the religion of the family even if they don't personally practice or adhere to it... a lot of people will join a church to get married or baptize a baby because it's custom but never really practice the religion beyond that.
There was quite a large survey done of religious and spiritual affiliation in Europe back 2005. Countries like Malta and Cyprus are still traditionally religious, but I think the boundaries have broken down somewhat between orthodox and unorthodox approaches. The UK is way down the list. The source below is a link to the survey. See page 9 onwards. It's quite interesting. It's a PDF.
EDIT: Abbreviations for the various countries are on pg 108.
These numbers are on how often people go to church:
Weekly 2,5 %
Monthly 4,6 %
Rarely 70,2 %
Never 22,4 %
Total 99,7 %
Only 8% believe that god created man
Christianity is doing pretty bad... religion is something that people are expected to keep within the four walls of home, it is something private. churches are left empty and people are proposing to close them down and use the buildings for other purposes.