The short answer, explained
Before issuing a VAT number, HMRC sometimes wants proof you're a real business intending to make taxable supplies, rather than simply taking your application at face value.
This is more likely for brand new companies with no trading history, applications for voluntary registration where turnover is still below the threshold, or sectors HMRC associates with a higher risk of VAT fraud.
The check itself usually involves a letter asking for supporting evidence: a contract with a customer, sample invoices, proof of a trading bank account, or a business website showing genuine activity.

