The ability to check a UK VAT number is available at: www.gov.uk/check-uk-vat-number.
This service allows users to check:
if a UK VAT registration number is valid; and
the name and address of the business the number is registered to.
The service also allows UK taxpayers to obtain a certificate to prove that they checked that a VAT registration number was valid at a given time and date. The certificate will provide valuable evidence for a taxpayer to prove that they acted in good faith should HMRC challenge input tax recovery or seek payment of lost VAT.
The European Commission website also includes an online service which allows taxpayers to check if a quoted VAT number from anywhere in the EU is valid. The online service is available at: https://taxation-customs.ec.europa.eu/