The primary objective of the Ultra Low Emission Zone (ULEZ) is to reduce emissions and improve air quality to improve health. Therefore, the number of exemptions available to the scheme has been limited, in order not to undermine the vital objective of the scheme.
All vehicles with historic tax class are exempt from the ULEZ. This tax class applies if a vehicle was built more than 40 years ago, with the date moving forward on a 40-year rolling system. This 40-year rolling age limit is set by the DVLA. This tax class excludes vehicles that are used commercially. In line with the existing Low Emission Zone scheme, all vehicles constructed before 1 January 1973 are exempt from the ULEZ, regardless of commercial use or otherwise.
I consider that retaining the exemption for historic tax class vehicles is the most appropriate mechanism to exempt vehicles of a historic nature, whilst preserving the scheme benefits.