Watch out for small companies invoicing you for VAT when they are not registered and pocketing your money. There is a handy little tool to check the validity of a VAT registration number at http://www.vatvalidation.com/ Simply enter the VAT registration number and it will tell you whether it is a valid number and if so who it is registered to.

Alternatively you can use an App available on the iPhone called Calc VAT which has a VAT Validator embedded within it.