Lots of businesses are being charged VAT by suppliers that are not properly VAT registered. This is dangerous as claiming the VAT back would be illegal.
To protect yourself from this you should check the Validity of the VAT number on the Supplier Invoice,
Using the link here http://ec.europa.eu/taxation_customs/vies/vieshome.do
Once you have confirmed the number is valid it can be entered in the Supplier ledger record to identify which traders have been checked. Anyone without a Valid VAT registration number can be set to a default VAT code to indicate that they are not registered and prevent you from accidentally claiming VAT on the invoices.