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Epilobium montanum has a four-lobed stigma. (I suspect that this is Epilobium montanum, but none of the flowers is sharp enough to confirm it using this character.) The other other willow herbs with four-lobed (as opposed to clavate) stigmas are distinctive. Epilobium hirsutum has much bigger flowers, and Epilobium parviflorum is distinctly hairy.
Thanks for that info. Sorry that the photos don't make it clearer!
Sorry - I forgot Epilobium lanceolatum (which doesn't grow around here). It also has a four-lobed stigma, but has narrowly cuneate leaves.
Lat/Lng: 53.62352, -2.35271
OS grid ref: SD767141