So, I'm just throwing this one out there to see what others think. I've photographed a several Goldcrests in the last few weeks and some show a noticably greyer nape and neck sides than others which may just be an indication of eastern origin. The only references to eastern birds I can find in literature is in A Guide to Warbler of the Western Palearctic, Parmenter and Byers that birds 'become paler and the wings slightly longer as the species ranges eastwards' but the Handbook of Birds of the World states 'geographical variation partly clinal, birds becoming darker and slightly larger from W to E' which is totally contradictory!
BWP states 'British birds generally darker and dirtier...with green-brown tone to nape easily seen (and, by contrast, grey nape of continental birds thus also obvious)' and 'larger and cleaner birds with noticably more striking wing bars (due to broader white tips occur in large falls of migrants on the east coast of Britain may be of the Siberian race coatsi or intergrades between it and nominate regulus'
Here are a couple of photos that hopefully illustrate my point. I'd be glad of any input!
Individual showing distinct grey nape and pale undersides - possible 'coatsi' or intergrade
Individual showing more green-brown nape - probable nominate 'regulus'
Another individual showing more green-brown nape - probable nominate 'regulus'