Nice pictures! It has to be a beetle larva, (caterpillars have "false legs" at the end of their abdomen, beetle larvae don't), but no idea what kind. Where did you find it? I'm sure one of the experts can help.
"Now my wife thinks these skills are apt for an entomologists dog, but our lawn is rapidly turning into something resembling the the Somme and I would rather she used her nose and digging ability to find something more lucrative - truffles would be nice."
Maybe you could get her (the dog, not your wife!) on a truffle-hound training course?
In some countries people eat beetle larvae - apparently they are nice toasted! See for example the page from this site: http://www.nhm.ac.uk/nature-online/life/insects-spiders/collecting-and-conserving/ct-scan-rhino-beetle/index.html It says:
"Larvae of rhinoceros beetles are fat white grubs, which bore in rotten wood, humus and compost. In many parts of the world they are collected as a high protein food, and in parts of Africa they are used to make an edible oil that is rich in unsaturated fats."