People don't realise that Lamb and Cattle slaughtered in the UK are automatically Halal, so long as the food is not contaminated by Haraam foods (pig, wine etc) even if they aren't slaughtered by a Muslim person. The term 'Halal' as used in stores is merely a recognition that the store does not sell any Haraam foods. So a Halal subway does not sell bacon or ham, and a halal KFC doesn't either.
If you thought the food you eat that is labelled 'Halal' means it was slaughtered by a Muslim person, you are very mistaken.
Anyone who understands Arabic and reads Quran will know this.