Where can I find car impounding laws for London?

I had my car impounded for leaving my car in a parking box with (no parking from 7am to 7pm, except for 20 mins) for 24mins. When I came back, I saw that the guys had tied the wires and were in the process of lifting the car. Is this legal. Should I not have just been issued with a tickect. Had to pay 260 to get my car back, 15 quid for the taxi and half a day of lost work. Seems really severe for a 4 minute delay!!!Can anybody tell me under what cirstances can somebody isuue me a ticket and not impound my car( parking issues)? regards