Pulling some of the above replies and comments together;
Based on your first comment
@cazy50, you mention your husband is self-employed. You then mention his 'boss' but if your husband is self-employed he does not have any boss. He is his own boss, which means any company he works for is his customer as
@JEREMY HAWKE states.
If your husband is not happy with the customer's rules then because he is his own boss, your husband can choose to not work for that customer any more and go find other customers to provide his services to.
Equally, your husband can choose to add additional charges to his invoices to his customer just as
@DWS stated. His customer might not like it though.
Looking at this from the outside, it appears a company (who you call your husband's boss) has called in a sub-contractor (your husband) to do some work, but the sub-contractor does not have their own van to deliver the service so they are renting their own vans to the sub-contractor.
Based on some of your comments above it is important to keep in perspective here; there is no employee and employer relationship here. No boss and employee - there are just two separate businesses doing business together. They can choose to continue to do business together or they can go their separate ways.