This little beetle landed on my red fleece and I was just quick enough to get a picture. You can see it has just landed as its wings are still poking out from under the wing cases at the back. It's black with four red/orange spots and is a a Four-spotted sap beetle, also known as a picnic beetle.
It earns that nickname owing to its preference for liquids such as beer, vinegar, fruit juice and similar, apparently causing it to ruin picnics by landing in them. I can't say I've ever seen that happen myself though and don't recall ever seeing this sort of beetle until now.