It does sound odd, I'll get more details tomorrow when I see him.
Edit, Compare the market says this :-
What is impound insurance?
Impound insurance (also known as compound insurance) is a type of short-term car insurance specifically used to release a car from the pound.
Standard car insurance doesn’t usually cover impounded cars, as it’s a specific, high-risk situation. So if your vehicle is seized, you may need specialist cover to get it back.
And Money Supermarket says this:-
Will my existing car insurance policy cover me if my car is impounded?
Probably not. Impound insurance is not covered by most car insurance policies as standard, so you will probably need to take out specialist cover.
Often these policies are issued for short durations (e.g. 7–30 days), and only provide minimal third-party cover.
News to me, car insurance making money again out of (admittedly self inflicted) misery.