Rousay, Orkney - seal sp. dilemmas

When I see a seal head bobbing about offshore in UK waters, I generally feel confident in calling the species; after all there are only two seal species found around the coast of Britain aren't there: the grey seal Halichoerus grypus and the common seal Phoco vitulina?

The fact that the grey seal has a distinct "Roman nose" profile and "W" shaped nostrils as opposed to the common seal which has a more rounded head, shorter muzzle and "V" shaped nostrils - should enable reasonable ID certainty in good visibility, shouldn't it?

The seal above, seen swimming offshore of Rousay is obviously a grey seal - the "Roman nose" profile an easily observed and prominent feature.
However, my confidence at ID is instantly undermined when a group of seals are hauled out on distant skerries, basking in the relative warmth of the overcast afternoon sun such as these beasts photographed at Savieskaill Bay, Rousay (photo left).

After all the colour variation appears somewhat wider than the palette described in my crib book - Butler J. Levin A., 1999 2nd Edition. Was it a whale? A handy guide to the marine mammals of the Hebrides. Isle of Mull. Brown and Whittaker.

The seal to the right of the picture shows what appears to be a fairly obvious "Roman profile" whilst the head position of the whiter individual to the left, seems more rounded? And just exactly how are those nostrils set - is that a "V" or a "W"? With the wind blowing both the 'scope and camera the subsequent shake blurs the finer detail. They simply are grey seals aren't they?