Hi,
I'm a newbie as well and as far I can find out UKAPU (a union of/for airsofters) requires you to have skirmished at least once before you can be a full member, although they allow you to join as a probationary member first. Also I'm not sure that they provide you with a defense, just a helping hand if you run into trouble whilst being a normal law-abiding airsofter
Their website is
http://www.ukapu.org.uk/website/home.php
and is a pretty interesting read.
The AOBA doesn't seem to have any recent information on their website and some other sources appear to suggest that it has collapsed entirely although I couldn't say for sure.
UKARA is database that retailers established and maintain to enable THEM to prove due diligence when selling RIF's.
For a valid UK defense I believe (please correct me if I've got this Arse-backwards) you only need to be registered as a skirmisher at a site.
As someone who is very keen not to be arrested for anything, including firearms offences, I intend to gain membership with my closest site as soon as they allow, (hiring for as long as nessercary) and register with UKARA and UKAPU as soon as possible. Then I'll probably buy through a local store.
I doubt I'll ever buy two tone because of my low budget; I'll save up for a better quality product that will hopefully be more reliable. By the time I've saved up I wont have to buy a bright orange HK33e
All this may seem very roundabouty-overly cautious, but my future career plans rely on a CRB, so better safe than sorry.
I realise I may have strayed off topic a little and I apologise. Anywhoo my two pennys worth.