You have two options when it comes to performing a VAT registration check in the UK. You could: Call the HMRC VAT Helpline on 0300 200 3700. This line is open between 8am and 8pm during the week.Use the VIES website, an online VAT checker for businesses in the EU. This website uses real-time data feeds from individual member states’ VAT systems.If the website shows a VAT number as invalid, you should double check with the company to make sure you have the correct number. You might also wish to inform them that the VIES site is displaying the number as invalid so they can contact HMRC to correct any problems with this.