Islamic law forbids Christians to make public display of their religion. Could that have something to do with this? Perhaps not, but what other group thinks Christian worship is immoral and wrong in itself, and has a theology of force and violence?
“‘Petrol bomb’ threats sent to churches and supermarkets,” BBC, January 16, 2019 (thanks to David):
More than a dozen churches have been sent “threatening letters” bearing a West Midlands postmark, with one letter warning of a petrol bomb attack.
West Midlands Police is investigating and said churches and supermarkets in the region and further afield had been targeted “over a period of months”.