What does ULEZ compliant mean?

ULEZ compliant means a vehicle meets the minimum emission standards set by Transport for London's (TfL's) Ultra Low Emission Zone (ULEZ). For petrol cars, this means meeting Euro 4 standards (typically registered after 2005). Diesel vehicles must meet the stricter Euro 6 standards (typically registered after September 2015). 

ULEZ compliant vehicles can drive in the expanded London zone without paying the daily £12.50 charge, making them essential for anyone regularly travelling into or through Greater London.