Dave's nailed it, Google was my friend but I do recall the reg. There were at least 3 furrin ones at Biggin when I went in '75 - 2 American and one Paraguayan, though I don't think it ever got to Paraguay. All in the basic RAF Transport Command scheme minus markings.
Quite a few Beagle 206s at Fort Lauderdale Executive when I went in '84, read an article about the owner who was doing them up and very keen on promoting the type...