Firstly: there is a charge for collecting and impounding your car. Provided that this is straightforward this would cost £150 for a car or light van. If the car was so damaged as to be difficult to pick up, or left in an unaccessible position, this could cost extra. If the car is indeed damaged you would probably not be able to drive it away but would have to contact a vehicle recovery operator. You may be able to find a local one on https://www.avrouk.com/
As well as this there are storage charges of £20 a day, charged from noon on the day after the car is impounded.
These charges must be paid before the vehicle is released. Pounds will normally accept cash, credit cards or debit card payments. If the car was impounded because it was being driven whilst uninsured, these must be made in person; payment will not be accepted over the telephone.
You are allowed to give up your rights to the vehicle. If you do this you will receive nothing back for it, regardless of it's value, and you may have to pay a disposal charge of £75, but you will not be liable for the initial £150 impound charge or any storage charges.
Please note that these are general guidelines only and they may vary from one police authority to another.