“It looked like just an ordinary handwritten letter on the outside. But when I opened it and read what it said, the horror of what it could entail became clear.” That’s Fr Andrew Browne, speaking to the BBC last week about a delivery to his church in High Green, Sheffield. The letter began, in handwritten capital letters: “Stop all your services straight away if you dont [sic] your church will be petrol bombed while in service.”

According to Fr Browne, at least 15 other churches have received the letters; police say other places, especially supermarkets, have also been targeted. The letters were mainly received in South Yorkshire, but the inquiry was transferred from there to West Midlands Police, after it turned out that the letters all had a postmark from the region.

Neither the diocese nor the bishops’ conference would comment on an ongoing investigation, but West Midlands Police told the Catholic Herald they are “investigating after several threatening letters have been sent to mainly churches and supermarkets across the region and officers are aware of a few sent further afield over a period of months. Enquiries remain ongoing.”

Whatever the outcome here, the episode has given rise to an uncomfortable sight: police standing guard outside churches.

It was reminiscent of scenes in France after the 2015 Charlie Hebdo killings, and the subsequent arrest of a man suspected of planning to attack a church. The French bishops’ conference and the police issued a joint statement, saying that “Every religious gathering, whatever its magnitude … is vulnerable today to acts of malevolence, which may extend to terrorism.” Those words were tragically vindicated the next year when a Normandy church was attacked – although God can bring good out of evil, and Fr Jacques Hamel’s death may yet lead to his canonisation.

In Britain, there is the same difficulty: finding a way to keep churches open and welcoming, and also keep them secure.