Did you receive an email with your Licence/Registration key and did you enter that key?
If you bought it directly via the avast.com site and the on-line payment processing, share*it then you didn't buy a fake.
Though you say you bought it through avast distribution for the UK, distribution is the same you either bought it via the avast/share*it on-line payment processing or you bought it through a distributor, which was it ?
If via a distributor you should also contact them, but also contact sales @ avast.com (without the spaces) and give them the full details, dates, email address used, etc.