This is the male of the sub species of Northern Wheatear known as 'Greenland' Wheatear. It is a passage migrant to the UK and only stops off here to refuel before making the most amazing of bird migrations from sub-Saharan Africa to Greenland and even the eastern seaboard of Canada, frankly astonishing! Additionally more recent discoveries from miniature tracking devices have also shown that it migrates across all of Eurasia to Alaska. One of the longest migratory flights known - 30,000km (18,640 miles). Alaskan birds must travel almost 15,000km (9,000 miles) each way - crossing Siberia and the Arabian Desert, and travelling, on average, 290km per day.
Superficially similar to the UK nominate race , but when compared side by side to the distinctly smaller local birds at this site leucorhoa is noticeably larger and brighter. If you are not comparing them side by side this can be subjective however I have found the most reliable field mark is the longer flared white supercillium as seen here ay at some angles appearing as min 'horns'. If you look at O.o.oenanthe you can see a much reduced supercillium that can widen at the end but never appearing long enough to form 'horns'. (see this image as an example of leucorhoa with horns here; http://www.pbase.com/davebarnes/image/147756490 and here http://www.pbase.com/davebarnes/image/143057486 and oenanthe without here; http://www.pbase.com/davebarnes/image/155922886)
Originally I thought this individual is the of the Icelandic morph, although since that comment the icelandic morphs have passed through and they are much less brightly coloured on the underparts. Now having done a bit of swatting up this would appear to be a classic male Greenland bird.