Normal size ladybird with 11 spots but with an obvious white edge to the sides of the elytra. Possibly white legs.
No interactions present.
This is a 10-spot, form decempunctata - the excess of black markings on the pronotum, the pale band around the edge of the elytra and the 1-3-1 spot pattern are all characteristic of the 10-spot, and not a Harlequin. Size is very hard to judge accurately, but about the mean ladybird length in Britain would be about 5mm
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I think the described size (I've assumed the 7-spot as the normal ladybird) put the Harlequin in mind, the other species being too small.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
Nonetheless, this is a 10-spot - Harlequin would have a slightly rounder shape, a plainer pronotum, much darker elytral lip, and different elytral spot patterns (the basis is 2-3-3-1, which puts the spots in slightly different places compared to the 10-spot's 1-3-1 even when not all the spots are present).
Size seems to be very difficult to accurately judge - when I do guided walks I often get people to estimate the size of the ladybirds we find and huge over/under estimations are amazingly frequent
Lat/Lng: 54.9643561, -1.3976979
OS grid ref: NZ386634