National Churchwatch, an independent group that advises clergy of all denominations on security, said priests are often targeted because they are considered unlikely to fight back.

Five vicars have been murdered in the past decade, and a 2001 academic study found that 12% of clergy had suffered some form of violence.

Nick Tolson, from National Churchwatch, urged priests to make themselves less obvious targets by removing their dog collars when off-duty. He has experienced resistance to this idea from some vicars, who see how they dress as a way of assuring people they are available to help.

Mr Tolson said: "For some clergy this is real radical stuff. The argument against it is it's their witness in the community - their way of saying, 'hello, I'm the vicar'.

"That's fine when you're being the vicar. If you're visiting someone or going to an old people's home, wear your dog collar. That means you're with people. It's when you're on your own, that's the key thing.

"There are times when you can be in church on your own and you look out and see some guy who's obviously off his trolley. You may want to slip off the dog collar before you see him.

"The local people know you're a vicar. They're going to talk to you whether you're wearing your dog collar or not."

Many attacks on clergy are motivated by money, and drug addiction is often a factor, he said. But some vicars will not seek to avoid potentially-violent situations and play down the risks they face.

In a survey of 90 London clergy Mr Tolson carried out last year, nearly half said they had been attacked in the previous 12 months. Mr Tolson said it was important to remind clergy they had a "duty of care to themselves" as well as to their parishioners.