Confidence: It might be this.
Notes: Until recently I'd have said C.populi with confidence, the other similar species (which lacked a black mark on the tips of the elytra) having been declared extinct, with the last record in the 1950s. C. populi larvae generally feed on aspen or sallow. However, there was a report that C.tremulae had been rediscovered. There is something at the back of my mind that the 'rediscovered' C.tremulae actually turned out to be something else entirely, but its a bit of a blurr.