The rates of people killed or seriously injured per billion vehicle miles for car users and motorcycle users are published in tables RAS30067 and RAS30066 respectively, available at: https://www.gov.uk/government/statistical-data-sets/ras30-reported-casualties-in-road-accidents#casualties-in-accidents-since-1979.
In 2017, there were 38 car users killed or seriously injured per billion vehicle miles in Great Britain, compared to 2,149 for motorcyclists.
In the road accident data, motorcycles include mopeds and motor scooters.
Please note that the number of serious injuries provided is as reported by the police. Since 2016, changes in severity reporting systems for a large number of police forces mean that serious injury figures are not comparable with earlier years.
On 19 July, the Department published the Road Safety Statement. The statement and action plan includes actions to improve safety for motorcyclists as well as rural road users, young road users and older road users. The statement is available at: https://www.gov.uk/government/publications/road-safety-statement-2019-a-lifetime-of-road-safety