I know this is a Dytiscid beetle, but can anyone help with a species? It was about 20mm long.
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Thanks for the id DD. I don't normally look at diving beetles so I am probably being a bit niaive here, but wouldn't size (approx 20mm long) rule out both dimidiatus and marginalis?
Lat/Lng: 51.385692, -3.34215
OS grid ref: ST066660