Sat on Greater Willowherb.
This is undoubtedly the Common Cockchafer (Melolontha melolontha). Summer Chafer is more compact with a much lighter brown thorax with pale brown hairs. Interestingly, the path between Dean Hill and Kelston Roundhill is the only place I have ever found Summer Chafer in abundance - about 20 years ago one evening I saw a dozen or so that seemed to be swarming around a Hawthorn - Mike Williams.
Simon Crampin, Mike Williams