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Could well be. I have got Chrysolina menthastri also coming up as the name for this beetle. Was your specimen high and dry in High St. or on a pond-dipping platform with water mint nearby?
Have since seen the comment about chalk stream
Lat/Lng: 50.9507, -1.8599
OS grid ref: SU099168
The Allen is a chalk stream, and parts of it are lined with water mint - and full of mint beetles!