Martin Herdman of course.
From an article on thisislondon.co.uk (1 August 2007):
“When traffic wardens started to blitz a quiet corner of suburban London, one shopkeeper decided it was his duty to fight back.
Martin Herdman put up a 1,000-watt public address system outside his shop in St Margarets, near Twickenham, and recruited a network of “spies” to alert him the instant they spotted a parking attendant in the area.
Then, as soon as the alarm was raised, he started playing a recording of a Second World War-style air raid siren over the system.
Mr Herdman’s early warning system gives customers a chance to move their cars before they are ticketed by the warden."