Confidence: It's likely to be this, but I can't be certain.
Notes: Probably the worst angle to take a picture of an Oil Beetle, but it looks like one - much easier from above or side when you can see the hyper-distinctive shape of short elytra and abdomen. Plus angled antennae. If you have a better pic it would be worth uploading, and someone may be able to get the species. Great find in Dorset by the way!