Confidence: It might be this.
Notes: Chris is quite right. Wing features are available, and are reliable for moths that meet all the criteria, but dissection of numerous 'doubtfuls' over the years has been a sobering experience. That said, I've never seen C.elongella with such an abruptly triangular costal spot. By the way, it is now some time since a C. elongella cropped up among the ones I've dissected: C. robustella certainly seems to outnumber it. Whilst C.robustella is at least bivoltine, C.elongella is (or was) univoltine.