In Ubuntu I installed the H.264 and MPEG-4AAC decoders in the belief that this is legal since the UK doesn't recognize software patents. Despite searching, I couldn't confirm this, so I've decided not to use them. It's difficult to uninstall the codecs so I'm simply going to not install them when I install Ubuntu from scratch next month. If you know the legal position on using patent encumbered codecs in the UK, please let me know.