We always used to go abroad in company cars but:
1. It was the only car we had so Dad was allowed to use it for any personal mileage including abroad. Dad had to go abroad with work anyway so sometimes flew, sometimes took the car over to mainland Europe, Ireland or Jersey so was covered for abroad anyway.
2. The fuel card only worked in the UK so as above he filled up at Dover and then was very frugal when we were away and we limped back to port.
3. Might be different rules with a van as it’s not a car that you could expect to use instead of buying a personal car. Also these days a lot of things have been clamped down on and companies are keeping better hold of their money.
I think you had better ask and obviously be prepared to pay your own fuel bills abroad.