Local authorities are starting to move or lay flat some unstable gravestones, after a number of accidents.

Lichenologists in Devon and Cornwall say the work would destroy rare colonies of lichen, which thrive on the surfaces of memorials.

Ann Allen, the British Lichen Society's records co-ordinator for the South West, said: "I think there are a number of alternatives to laying gravestones flat.

'Bridge the gap'

"Cost is one of the problems, but gravestones can be secured in various ways with bars or they can be dug in better."

Carol Simpson, ecological adviser for the Diocese of Truro and the co-ordinator of Living Churchyards project, said: "Each churchyard has to be treated individually because the parochial church councils are responsible for their churchyards.

"If the churchyard is closed, it is the responsibility of the local council.

"I am trying to bridge the gap between the conservation bodies and the diocese so that people can make informed decisions."

The British Lichen Society will debate the issue this month.