Transport for London says it is aware of a specific group of drivers who persistently refuse to pay multiple outstanding penalties. Recent data shows that 94 per cent of the outstanding debt is from persistent evaders. When there is no response over an extended period from a driver who has incurred a ULEZ charge, the enforcement process is triggered. Action to recover the debt involves enforcement agents visiting a home address to recover money owed. They can also seize particular belongings and use the proceeds of a sale to satisfy any outstanding debt, for example clamping a vehicle and selling it at auction.