sorry, forgot to mention
Organisation like the Scouts, Cubs, Guides , Schools and many others have memberships with Groundspeak, All of which will also claim VAT back as they do not have to pay it. This is why VAT number must be shown on any invoice. With out it it's worthless to them.
There is nothing people can do with your number, its not a secret, every company letter i send has it printed on the bottom .
another snippet
VAT invoices: what they must show
If you are registered for VAT, then whenever you supply goods or services to someone else who is also registered for VAT you must give them a VAT invoice.
look here for yourselves, great resource
http://www.hmrc.gov.uk/vat/managing/charging/vat-invoices.htm
To break the Law unknowingly is a defense, to do it knowingly is expensive
Please note, I love caching and only trying to help.