Mileage claims with car allowance - Europe / Germany

We are currently applying a policy of a reduced mileage claim rate for employees who are also in receipt of a car allowance.

This is currently in place for employees in the UK, France and Germany, but not in the Netherlands, since our understanding is that we are not permitted to make this adjustment in this location.

So far, this has worked fine, but we are now starting to receive questions in Germany that this is not usual practice (new joiners are highlighting this is not something they have experienced elsewhere).

Does anyone have any experience on what is best practice in Germany, and/or what is permitted?

Thanks in advance Thumbsup