HM Revenue & Customs

Can I use my existing User ID and password to register for business taxes online?

Yes, but only if you signed up for an organisation Government Gateway account when you got your User ID and password.

If you signed up for an individual Government Gateway account you'll need to get a new organisation User ID and password before you can register for business taxes (Self Assessment, Corporation Tax, PAYE for Employers and VAT).

The User ID and password for your individual account can still be used to access the online services you are already enrolled for.