Back on topic
Visited The Bourne yesterday, was unable to find the grave on first search. However the very helpful ladies in the office at the modern St Thomas' church have a full list with a hand-drawn map compiled by the West Surrey family history society in 1988. Thus armed with copies I returned, located the grave and gave it a bit of a tidy-up. I intend to keep an eye on it from time to time and will see if I can improve it despite not being a gardener!