Using your own car for work
Under certain circumstances, an employee can be paid a tax-free allowance by their employers when using their own car, van, motorcycle or bike for work purposes.
It is important to note that this tax-free allowance does not include journeys to and from work but is relevant to employees who use their own vehicles in the course of their work such as for making deliveries, visiting customers and prospective customers.
Employers usually make payments based on a set rate per mile depending on the mode of transport used. There are approved mileage rates published by HMRC. The approved mileage allowance payment rates are available where an employee uses their own car on a business trip. Where the approved mileage rates are used, the payments to employees are not regarded as a taxable benefit.
Where an employer pays less than the published rates, the employee can make a tax relief claim for the shortfall using mileage allowance relief. For all cars the approved mileage allowance payment for the first 10,000 business miles is 45p per mile and 25p per mile for every additional business mile. An equivalent system at 20p per mile is available for bicycle travel and 24p per mile for motorcycle travel.
There is an additional 5p per passenger per business mile for carrying fellow employees in a car or van on journeys which are also work journeys for them. Only payments specifically for carrying passengers count and there is no relief if you receive less than 5p or nothing at all.
Source: HM Revenue & Customs | 25-05-2017