VAT compliance

I have spoken to a few different people on this issue and still have not got a clear answer. So here we go, my son buys and sells second hand cars for cash. His sales are limited to cash buyers £2-4k I have setup a new business and licensed to FCA registered to finance cars. I basically want to help him sell more up market cars £5-10K via the new ltd company and finance licence but without combining the 2 business together. How do I go about this without attracting VAT and to sell them on his behalf. Can he give the cars to me on a Sale or Return basis? Or is there another option with buying the cars from him and possibly having to change the V5?

thanks for any feedback