I’ve heard that Scandinavians actually have darker skin than people in the British Isles, and can produce more melanin and burn less. I’m not sure it’s true though because I’ve seen some very pale people from Scandinavia. In fact, Scandinavians look pretty much the same as British and Irish people to me. I couldn’t tell what northern European country somebody was from just by seeing a picture of them.
Picking the nationality of a single person 100 % of the time is not possible, but there are certainly “looks” that I think would help you guess better than random, with experience.
There’s a wide range of skin types in all the countries, but I can’t find any data that could be used to say wether the averages match the claim you refer to.
Been readin’ Ben Franklin, haven’t you? 
I actually think the UK (not counting immigrants and their descendants) has more “Mediterranean” looking people than Scandinavia does. Like Cheryl Cole for example, or a lot of my relatives, my ancestors are from the UK and Ireland.