Confidence: It's likely to be this, but I can't be certain.
Notes: I also wondered about S.rhombeus, but it seems to me that the thorax is too long in comparison to the wings for this species. Size would help of course: it is normally a whopper of a click beetle - close on 20 mm body length. Athous campyloides is smaller (c.11 mm). It has a long, almost parallel-sided thorax. I can't entirely eliminate other Athous species though, such as atypical A.bicolor or even A.haemorrhoidalis which hasn't fully coloured up.