I would go to your HR department to find out the lowdown on this - a company car is taxable too so you will be paying quite a chunk each month. On the other hand, you will no longer have to pay for maintenance, car tax, insurance, repairs etc - make sure that the company is insuring your car on a fleet policy. They can't change your contract without telling you, but if it's more economical for them to provide you with a fleet car, then I can see why they might want to.