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That was tricky! I had a look at various web images of both and to my untrained eye it was a very tough call, but I think The Straw Underwing looks a better fit. Based on an overall grey rather than brown base colour, and the much lighter grey tones on the rear edge and clearer whiter cross lines.
Thank you both so much for your help on this one and sorry I couldn't show better images of antennae or hindwing that may have made ID easier!
Kind regards, Martin
Lat/Lng: 51.696, -0.3662
OS grid ref: TL130009