Taken from PRSformusic, UK.
"In the UK, all original music is protected by copyright from the time it is recorded/written down in some format."
and
"Post a copy of the recording to yourself by special delivery. Clearly mark the envelope so you know what music it holds, but keep it sealed.
and/or
Store a copy with your solicitor or bank manager. Remember to keep a receipt and be aware that this method is likely to cost you some money."