After some internet research this beetle was identified as a Golden-bloomed Grey Longhorn Beetle (Agapanthia villosoviridescens) A pair mating were seen on a Hogweed leaf near the 'Dragonfly Pool'
In the research it has been mostly reported above the Thames Valley and to the east.
Golen-bloomed Grey Longhorn Beetle Agapanthia villosoviridescens ©Dluogs
Repoted to the national recorder of Longhorn Beetles Dr.Rejzek (Martin.Rejzek[AT]jic.ac.uk)His reply was "Agapanthia villosoviridescens seems to be expanding its range in the UK. I am getting increasing numbers of records from outside its traditional strongholds in East Anglia".
It also looks like it is the first time reported in the Blackwater Valley.