Q: the movie i want to download is only available in the US can I download it for use in the UK

No, you can only download from your country's store - to download from another country's store you need a valid billing address in that country and be in that country at the time of purchase. You can try requesting that it be added to the UK store, but ultimately it's the film distributor that will have to grant Apple a licence to sell it here :  http://www.apple.com/feedback/itunes.html