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R. strigosus has yellow pleurae, of which there's an indication in your specimen, but the frons should be much narrower. Most of the British records of strigosus are from the chalk, so that wouldn't fit with your Scottish site either. I think this is most likely a slightly teneral scolopaceus, but the wing looks rather broad (could just be foreshortening), and I'm wondering whether it could be latipennis? It would be interesting to hear other views on this, from those who are familiar with that species.