I have just posted a reply on your other thread Luke, but to answer your question about Instructors Ratings, the UK is one of the few countries in the world that actually give you credit for foreign instructing experience. You would have to do some flying with an FIC (Flying Instructor Course) instructor until he is satisfied that you can pass the flight test, yes there would have to be a separate instructor test. If you meet the requirements for an FI rating that is waht you would get.