Best stick with N-reg, Andy. Someone got G-ANDY 40 years ago, on a Dove, and it crashed in 1962. Nor could you have G-AUSI or G-AUSS, because those would have been Australian registrations prior to 1929. Unlike the FAA, our dear CAA doesn't allow re-allocations, transfers of registration or re-use of 'British Colonial' registrations long since surpassed by State systems, though I've never understood or believed the lame explanations they put forward about possible ATC confusion of aircraft type. Whatever aeroplane you are able to afford in the future, I doubt that it would be a Sopwith Antelope like 'AUSS.