needed a solution to a growing parking enforcement problem. The city towed ticketed cars to the pound, where they were often vandalised. Those whose cars were damaged sued the city for losses and the police had to itemize everything in the cars. Dan Stills, head of the city's traffic division, thought an immobilizer would avoid the expensive towing problem and approached Marugg with an idea to improve on the device to keep the cars where they were parked. The Denver police first used the wheel boot on 5 January 1955 and collected over US$18,000 (US$ in dollars) in its first month of use. Although the wheel boot was first cast in steel, Marugg soon switched to a lighter aluminum-based alloy. Marugg later sold the device to parking lot owners, hotels and ski resorts, as well as a Jumbo version for farm equipment and larger vehicles. The Smithsonian Institution now has a copy of Marugg's boot on display in Washington, D.C. By 1970 Marugg had sold 2,000 boots. Although the patent ran out in 1976 and modern car and truck wheels necessitated a redesign, Marugg's daughter kept up the business until 1986. Clancy Systems International later bought the rights to the boot. The boot allowed Denver to maintain one of the largest collection rates for parking fines of any city in the US through its first fifty years. The Denver Sheriff ran the "Boot Trucks" for many years until the detail was transferred to Denver Parking Management. The best known wheel clamp in the UK is the 'London Wheel Clamp'. The designer, Trevor Whitehouse filed the patent in 1991. He originally called the device the 'Preston', after his home town in Lancashire. Primarily used on private land, its notoriety grew once it was introduced to public roads under the Road Traffic Regulations Act of 1991 (commonly known as the de-criminalising of the yellow lines act). The first areas in the country to be decriminalised were the 33 London Boroughs during 1993/94, hence the name change. Controversy Wheel-clamping is notoriously unpopular with unauthorised parkers. While a traffic warden or police officer has jurisdiction over public roads, in many countries, the law allows landowners to clamp vehicles parking on their property without permission. One British man became so annoyed at having his car clamped that he removed the clamp with an angle grinder. He subsequently received publicity as a self-styled "superhero" called "Angle-Grinder