Expenses and benefits: business travel mileage for employees' own vehicles
4. Passenger payments
If your employee carries another employee in their own car or van on a business journey, you can pay them passenger payments of up to 5p per mile tax-free.
You won’t have to report this to HM Revenue and Customs (HMRC) or deduct and pay National Insurance on them either.
There’s no equivalent to Mileage Allowance Relief (MAR) for passenger payments.