No interactions present.
The appearance of a slender, slightly upturned bill, plus the finely spotted upperparts, is typical of a winter Red-throated. The forehead is gently sloping, too, rather than quite angular, as in the two larger common divers.
My Flickr photos...
Although you can't see on these photos, there was definitely no white flanks, which lead me to rule out the RTD & BTD.
That is primarily a feature for distinguishing Black-throated and Great Northern. Red-throated often sits low in the water and looks like this bird. Like all such features, it is only one criterion to use along with others in order to arrive at an ID. The overall appearance of this bird is of a rather gentle diver; no heaviness or angles, really, if you know what I mean.
If you had seen a Great Northern close in, the huge size would really have struck you..they are an impressive bird!
Lat/Lng: 54.6345, -5.5312
OS grid ref: NW722323