hi glosguy,
rene is correct the invoice the dealer would produce would list the vehicle and any additions net and then charge vat on the total @20% for an average customer. so the exemption will apply to the full “invoice price”.
as it would for any servicing and repairs. the vat 1615a and supporting documents would have to support the dealers sale.
i would just make sure you have copies of any and all documents before and after the sale. if your prepared to wait you could ring the vat support line but be aware there are long queues. i work for a firm of accountants and i spent 3 hours this morning in various hmrc queues lol.
i will ask our vat partner what he knows about this tommorrow let you know in the pm.