from the TFL site:
Historic vehicles
You can apply to stop paying vehicle tax if your vehicle was built more than 40 years ago. This date moves forward on a 40-year rolling system. Assuming the rules stay the same, when the ULEZ launches in April 2019, vehicles built before 1979 will be eligible to apply for historic vehicle tax class.
All vehicles that have a historic vehicle tax class will be exempt from the ULEZ. This tax class excludes any vehicle used commercially (for example, coffee vans or street food vans).
In line with the existing LEZ discount all vehicles registered before 1 January 1973 will be exempt from the ULEZ, regardless of commercial use or otherwise.
If your vehicle meets the above criteria and is registered in the UK, it is automatically exempt and you don't need to register with us. If your vehicle meets the above criteria but is registered outside the UK, you are also exempt, but will need to register with us. Details on how you can register will be available closer to the time.
