Good morning guys, I cannot find any information on VAT registration when the owner of 2 entities are the same.

Say for instance an individual owns 2 companies - the one sells parts and the other does services. As far as I remember there used to be an anti-avoidance rule then obligation you to add the two's turnover together when considering whether to register for VAT. Same as when some of the business is in a sole prop and the other in the Pty.

Does anyone know where I can read up more on this?