From a tax angle, if the car is owned by an employer, the employer is responsible for all upkeep on the vehicle. Similarly, if you use their car for business-purposes only (i.e. they specifically state in your contract that the car is not to be used to travel from your home to the place of business), they should either provide all fuel or reimburse you for purchasing it. If the employer is adamant that you have to pay for things like tyres and fuel etc., I should have a chat with someone at the Citizen's Advice Bureau as it seems you are being taken for a ride - no pun intended!!