as 8moss obviously works for Enterprise why not now send out a group U4 wide email asking each rental employee how much they can claim back - even if they can claim back?

Over 50% will say nothing I assure you. And here I believe is the heart of the problem in that there is a clear lack of communication and miscommunication from all at Admin level - mainly insulated and without an understanding of rental (include all level 3's here)- how do you expect them to do their jobs correctly?

Tell your employees then can claim £5back.