'You can apply for exemption from paying vehicle tax if you get the:
higher rate mobility component of Disability Living Allowance (DLA)
enhanced rate mobility component of Personal Independence Payment (PIP)
enhanced rate mobility component of Adult Disability Payment (ADP)
higher rate mobility component of Child Disability Payment
War Pensioners’ Mobility Supplement
Armed Forces Independence Payment
The vehicle must be registered in the disabled person’s name or their nominated driver’s name.
It must only be used for the disabled person’s personal needs. It cannot be used by the nominated driver for their own personal use.'
https://www.gov.uk/financial-help-disabled/vehicles-and-transport