Hi all,
It is a female Great Green Bush Cricket (Tettigonia viridissima) late stage nymph (the adult is fully winged, and it is a female because of the ovipositor). They are relatively common along the south coast and in the SW. you often get them in gardens (in pampas grass clumps, hedges etc) and they stridulate very loudly at night. They eat anything and can allegedly bite, like the closely related, but much rarer "Wart-biter". The full grown adult is a bit of a beast, about as big as a full grown locust.
cheers Darrel