It was very small (approx 2-3 mm) and quite fast moving so it's not impossible that it was actually a beetle whose wing cases we didn't get a look at.
It was found yesterday, weather was very warm. IT was on the brick edging of a gravelled patch of garden.
You can't entirely tell from the photo (sorry, it wsa just taken on my phone) but it's front leg pair came from the "neck", then there was a large gap before both back leg pairs came together. When flipped gently onto its back, its underside appeared smoothe.