My wife is a Buddhist meaning atheistic humanist. She belongs to a militant Japanese sect whose aim is to convert people. She is having a great amount of success because people in Britain, nice and polite as they generally are, are not Christians. Her converts are nearly all Catholics and Anglicans who have left there childhood beliefs with no twinge of regret.
Further, both my mother and father, unchurched Anglicans, died with no signs of repentance or appealing to God's mercy.
Further, the Daily Mail and Daily Telegraph are both old fogey papers that like to talk about decline in all sorts of areas. Christians, according to their lights, would be three wheeler ones. There is a decline among those.
If I am a Christian then Britain isn't as a whole.