A terrorist attack in the UK is "highly likely" following attacks in other parts of Europe, a five-judge tribunal has heard, as churches in Britain are told to tighten security after the murder of an 85-year-old priest in Normandy.

The heightened state of security comes as images threatening attacks in London and other major world capitals were reportedly posted on Telegram, a messaging app used by jihadis.

Despite there being no specific intelligence relating to attacks against the Christian community in the UK, the National Police Chiefs' Council is urging the community to be alert but not alarmed, report concerns and review their security as a precaution.