Since no one else has answered yet, I'll jump in and be the first to show my ignorance. It actually never even occurred to me that there would be a difference in the tank fittings. I would think the BEST source of information would be other Airstream owners in the UK - there are more than just a few of them, and surely they have faced the same dilemma. Perhaps one of them will see your message on this forum and give you the solution to the problem. IF an adapter exists, I would think you'd only find it over there. If there is not one on the market I would think that, in theory at least, a good machine shop should be able to make one. However, making anything for such fuel systems may require special licenses and permits, and finding someone to cobble up a part that will work may be a practical impossibility.
Mike & Diane
"The written word will soon disappear, and we'll no longer be able to read good prose like we used to could." - James Thurber