I'm getting married in less than a month. I've lived in the UK for just about 8 years, but still have close ties to all my American family and friends. We originally tried to set up a John Lewis's registry, but it would only let us put stuff on there 6 weeks in advance - we never added things to it it, but they sent us the the registry cards that you put in your paper invites last week. If I had only sent out invites 1 month in advance, I don't think I'd have anyone actually make it to my wedding due to time of year and overseas guests.
So we set up on amazon.co.uk one and it's worked out so well. You can also add things from other websites, not just amazon. Also, amazon uses couriers that will actually deliver to the Highlands, unlike a lot of websites. We don't need anything for our house, but decided that we'd rather let people know that we'd happily accept big bags of chicken poop for our allotment, rather than some useless serving platter thing, etc. (Not that we wouldn't happily accept this either, just it's harder to 'let go' of). We've been having gifts trickle in from the American and British sides and it's as easy as can be. Plus you can just keep an eye on the stock (John Lewis's main reason that things go out of stock and change, so they want you to have the latest and greatest) so if something goes off the site, you can just change it.