There are several reasons why the police can seize a car and take it away to a pound. Here are the main ones -
Many uninsured drivers are fully aware that they don't have cover in place but they still take the risk. However a lot of motorists think that they are insured, but are not. The problem, usually, is that they are using their car for a purpose which is not included on their cover notes, such as:
If a motor vehicle is not in use it must be stored somewhere where the public have no right of access, such as a garage or private driveway, and the DVLA must be informed by applying for a Statutory Off Road Notification (SORN). In addition, under the Continuous Insurance Enforcement (CIE) regulations of 2011 it is illegal to own a car which is taxed, but not insured. This means that you must cancel any tax on a SORNed vehicle and this helps the police to keep a check on which cars are street-legal, and which are not.
In short: if a car is uninsured and on a public highway it is open to seizure, whether it is used or not.
If a motorist drives a class of vehicle which isn't included on that person's licence, then the vehicle may be impounded, whether it is insured or not.
Causing, or being likely to cause, alarm, distress or annoyance to any members of the public is an offence. This could include, whilst stationary, playing music too loudly, revving the engine too hard or even just running the engine for too long whilst parked. If the vehicle is moving it could include splashing someone by driving through a puddle, tailgating or excessive acceleration or braking. It is mandatory that the motorist concerned is warned IF POSSIBLE, for a first offence, that a repeat of a similar offence could result in the car being impounded; this is known as a Section 59 Notice. This can be in addition to any other penalty for the offence. If a police officer feels that a driver is indeed committing a similar offence within 12 months of a Section 59 being issued, OR within 12 months of one that would have been issued had it been possible to do so, then the vehicle can be seized. This is increasingly being used to stop 'boy racers' who cause annoyance or potential dangers to other people.
If a vehicle is parked in a position in which it is causing an obstruction or potential risks to other road users; whether it is broken down or not; it can be taken away by the police after they feel that a reasonable time has been allowed for the owner to move it.
A uniformed police officer is entitled to stop any motor vehicle, at any time, for any reason. A motorist who fails to do so, stops for less time than is necessary for the officer to make any necessary enquiries, or runs off before those enquiries have been completed, leaves the vehicle open to being seized.
If a police officer has reason to believe that a vehicle has been used during the commission of a crime, and that it, or it's contents, may be used as evidence, it can be impounded.
A vehicle which is registered from abroad may, provided that is is insured and street legal, be driven in the UK for a maximum of six months unless, usually, the driver is a permanent UK resident. If it is still on our roads after this period; or if the permanent resident has failed to re-register, tax and insure it; it is subject to being seized immediately.