It is quite normal practice for employees to be reimbursed at a reasonable mileage rate for business use of their own vehicles. Please see the below rates of HMRC approved mileage rates:
Mileage payments do not need to be reported on a P11D unless the employee is reimbursed at a rate higher than those approved by HMRC, as stated above. If the employer pays less than these rates, it is possible for the employee to claim income tax relief for the shortfall, please click here for further details on how to claim this from HMRC.
Rates of up to 5p per mile, per passenger, are also allowable when paid for the carriage of fellow employees on the same business trip. This now also covers volunteers who drive for hospital car services etc, even though they are not strictly employees.