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This is an unusual find, I suspect that it is a Southern Field Cricket. The wings look a bit short for this species, but they could easily be damaged. These crickets are not native to the UK, but they are commonly used in the pet trade as reptile food. Apparently they can at times form temporary colonies in this country, but it may just be an individual escaping from someones home.
I'm not 100% sure about the identity as I've never seen this species before, but the people here -
Orthoptera Recording Scheme - Home should be able to confirm it. They'd also probably be interested in your record, there's an online recording form here -
Orthoptera Recording Scheme - Sighting if you have time.
Guy