Contact your local council who will come out and put a 7 day order on it.
During this time they and the police will try to contact the registered keeper. If the registered keeper can't be found or takes no action the vehicle will be taken away.

When you contact the council register your interest with them for the vehicle. They could then offer it to you to save them coming out to collect and dispose of it.

Apply for a new log book and its yours.

If the vehicle is on private property the 7 day order has to be extended to 15 days.

Thats as far as I understand the procedure to be