Anyone know of any more northerly grapefruits?

From the Home Citrus Growers site I recently discovered:

World's Northernmost Fruiting Grapefruit? (Home Citrus Growers)

Anybody know of anything further north than London (there's a claim for Porlock, but if you're going to make fruiting a criterion I think you have to actually ripen the fruit)? Really I think the UK is probably the only place with a shot at growing it this far north. I've seen some kind of citrus growing in a greenhouse in Iceland (I can't recall what it was) but I think to count it really has to be outdoors...where's the challenge in growing it in a greenhouse...even if it is an immensely cool greenhouse heated only by infernal depths of the earth.