The above two shots are of British Eiders in Britain with their greenish bills and no evidence of sails.
Northern Eiders in Iceland. The males have prominent yellowy bills and obvious sails on their backs. Most of the females were rufous with some also showing a hint of a sail on their back. A few females were paler and didn't show any hint of sails. I thought these could be either a different race or a different age.
The male on the right had a bright yellowish bill with no sails, like the Llandudno bird. I think that bird was probably a British x Northern Eider in retrospect like this bird. In Iceland most male eiders appeared to be Borealis with a few British type birds. It only makes sence that some genetic cross-over will occur.