If you’re bringing a second-hand vehicle into the UK, you don’t have to pay VAT. As long as you paid VAT in another EU country when you bought it, but you must still complete a NOVA (notification of vehicle arrival) notification to HMRC within 14 days of the vehicle arrival.
If you normally live in another country in the EU and bring a vehicle with you on a temporary visit to the UK, you don’t need to notify HMRC. As long as your stay is for less than 6 months in a 12 month period.
If you are on a temporary visit but decide to permanently register your car in the UK you have 14 days to notify HMRC after your decision.