The reason Christianity is going downhill in the UK? The chuches are adopting to the prevailing liberal culture, rather than be an agent of counter-culture.
Here is a quote that pretty much sums up the article:
91% of responses followed a uniform theme that the decline in traditional Christian moral and doctrinal teaching has caused the outflux of congregations. They listed the lack of apologetics, the reasoned defence and explanation of Christian doctrine, as one of the main reasons for the collapse. “It’s a myth today that the people of this country have rejected Christianity; they simply haven’t been told enough about it to either accept or reject it,” wrote one respondent.