Largely it will depend on the contractual basis they had the car on and if it was very clear that it was mileage / role dependant. Even if you were clear it’s a huge step to take away a car without some form of Transition arrangements.some organisations would pay and others would allow 6-12 months usage.

it’s relatively unusual to ring fence them and then pay them more   

On top of Keith's point, I'd add that there has, historically, been an element of status involved in being a company car driver that cannot be overlooked. If company cars are associated with senior managers, directors, key sales leads and similar, then losing a company car can represent a perceived loss of status that, in a change management scenario, may result in a disagreement over what constitutes suitable alternative employment.

Just one more reason why employers are increasingly moving away from company cars and into car allowance payments.

In reply to Keith:

• Hi Keith, thank you. Yes, we are going to allow 6 months usage after being in the new role (which doesnt requiere a car). Sorry what do you mean by ring fence and payment? To clarify, it is a new role and the main additional responsibility is managing a regional team. They wanted to keep their options open and for them to have the opportunity to opt out/redundancy if the new role doesn’t appeal to them. These new responsibilities will be rewarded with 8% salary increase.