To tax a vehicle in the UK, you will need to provide the DVLA with certain information about the vehicle and yourself. This can be done online, by phone, or at a Post Office that offers vehicle tax services. You will need to have valid insurance, an MOT (if applicable), and a V5C registration certificate or the green ‘new keeper’s slip’ that you will receive when you purchase the vehicle.
In terms of when to tax the vehicle, you can pay for road tax at any time before or after you have collected the vehicle. However, you will not be able to drive it on public roads without valid road tax. You may be able to get a refund on any unused road tax that was paid by the previous owner if the tax disc is still valid.
If you have any further questions or concerns, you can contact the DVLA by phone on 0300 123 4321 or by using their online contact form on their website.