Confidence: It's likely to be this, but I can't be certain.
Notes: I can see the similarity to Marsh Pug (and knowing the size would be helpful), but based on the wing markings and the shapoe of the wings I think this is Common Pug. The post-median line is not as clear on this example as it is sometimes, but I think the characteristic zig-zag in the line just before it meets the costa (leading edge) of the wing is still apparent. The costa is more rounded than that for Marsh Pug. Would be good to get views from others though, I've never seen Marsh Pug in the flesh.