I was told you must have no contribution at all to the other business in any way that it functions.
Pretty much, there need to be no link from one to the other. Whilst technically you can do it, to be able to achieve it in reality would be impossible.
You cant share anything, not even a pen or a swivel chair.
The only way you can do it is if you prove its for commercial reasons, so maybe if you had 1 company down south and another up north, one being window cleaning another being gutter cleaning with separate staff, websites, customer bases etc you might be able to do it.
But again it's so dodgy, if a customer from business A puts you into a job that you complete via business B, there's a link and would be so hard to pull off you would spend all your time worrying about artificial separation.