In the UK there are 3 things your car must have before you can take it on the road. First, your car, if it is more than 3 years old, must have a valid MOT certificate, your car must have insurance and finally, your car needs a Vehicle Excise Duty disc which must be displayed in the windscreen. All this information is available to the police and is held by the Driver and Licensing Agency, otherwise known as the DVLA. The DVLA is a government agency which is part of the Department of Transport and its role is to keep a database of all registered vehicles and licensed drivers.
When you buy a car, you will need to fill out the registered keeper form and return this to the DVLA. You must also purchase insurance and make sure that the vehicle excise duty or tax disc is valid. Failure to comply with any of these is an offence and you can be fined or even taken to court and prosecuted. When your tax disc is due to expire, the DVLA will send you reminder through the post and you can purchase your new tax disc at the Post Office, online or by post from the DVLA directly. The amount you have to pay depends upon the type of vehicle and this is something to be aware of when purchasing a car so that you can budget properly.
You may wish to take your vehicle off the road for a period of time and if this is the case, you must declare this and fill out a statutory off road notification or SORN. If your road tax runs out and you do not declare a SORN, you will be pursued for road tax. You will need to renew your SORN every year unless you re-tax the vehicle so that you can drive on the road again.