We had a Sea Eagle down here in W Sussex last year which I saw twice during the winter. I though it might be an escapee from some ones private collection but no one reported it missing. Spoke with a chap from the RSPB and he said they'd had a similar thing a few years previous down in Wiltshire. There. they'd had some twitchers spot it and were able to identify from leg rings that it was a juvenille male that had flown over from Scandanavia. It over wintered and then went back. Although probably not the same bird, the one I saw was probably a similar type of thing.
Makes me wonder,,, do young male Sea Eagles have a gap year and go globe trotting?