HMRC is the short form for Her Majesty's Revenue and Customs, and you guessed it, is the UK tax authority. When you are getting VAT registered in UK you get an online HMRC account. So if you would have done this individually you would have gotten an account, but in this case as we are acting as fiscal agents for many clients in UK, we have only 1 account for all of them. We can't give access to this account to our customers because it contains sensitive data of all our clients.
The HMRC online account contains data like VAT returns submitted, VAT due or refund due. VAT due is shown when VAT return is submitted but payment is not made.