From the photo in the article, this terrorist couple do not appear to be of Anglo Saxon or European ethnicity. Seems likely that she was an immigrant to Britain in her childhood and raised by Islamist parents.
Over the past several decades, younger generation Brits (and Irish Catholics) have abandoned traditional Christian church attendance. Churches are empty except for the occasional wedding, baptism and burial services. There is no Christian influence on immigrants so they pursue their own extremist traditions without fear of being ostracised. The Queen, as head of the Church of England has no authority or influence. Sad and troubling.
No doubt true of some, but by no means true of all. There are plenty of Christian immigrants to the UK, though you wouldn't know it from reading what appears here.