Hello, I am Keith, one of the experts on Just Answer, and pleased to be able help you with your question.
The Turnover Level for VAT Registration is 83K in any one year. Below that no registration is needed. If you do as you suggest you could restart with a blank sheet. HMRC might view it with a jaundiced eye, but there is nothing they can do about it.
I do hope that you find my reply of assistance.
They might try, but were it operated be two separate legal entities as you suggest then that Department would have to lump it. They won't like it though!