No interactions present.
It's certainly between P. elegans, P. longirostris and P. serratus. Without seeing the ventral teeth (the ones on the front edge of the rostrum), it is difficult to tell. Having stared at the Collins Pocket Guide to the seashore, A Student's Guide to the Seashore (Fish & Fish) and MarLIN for confirmation, on balance I think it is P. serratus and have added my agreement to that ID. The end of the rostrum is more curved up in P. serratus than the others so that was the feature that tipped me towards that ID. The photo is very good, clear and helped towards some sort of identification.
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Lat/Lng: 50.7572, 0.1551
OS grid ref: TV521975