Copyright is an automatic free right in the UK so there is no need or legal requirement to register it. There is no official registration scheme in the UK and although several exist, the IP industry has generally been of the viewpoint that they are of limited value to the general public.
Liam could finish his posts with 'Copyright [real name] 2014' or '(c) [real name] 2014' to make it clear that they are a copyright work, and even go so far as to add a disclaimer such as 'All rights reserved. This work must not be reproduced in whole or in part in any format without the written permission of the copyright owner.'
But if someone contested it with a date stamped document and a witness, his would be the weaker argument. Unlikely as it seems, a post on the internet isn't the strongest case in a court of law because the code is open to manipulation.