Perhaps, forwarding this discussion to the Nextbase legal department would be a better option, to check if it is legal to impose an advert on copyrighted material, without the copyright owner's permission.
Here is what it says regarding copyright infringement on the Gov.uk website:-
Question - I want to stop someone using the image I created in a way I do not approve of, or have not approved
Reply - If somebody is making use of your images without your permission, there are a number of options open to you as the copyright owner. Although you do not have to, it is usually sensible to try to resolve the matter with the party you think has infringed your copyright. This may save you time and money, and it may be necessary to show a court that you have tried to solve the matter with the other party. Mediation is one way of resolving an issue before starting court proceedings. The IPO offers a mediation service which can help to resolve intellectual property disputes – including copyright – without going to court: https://
www.gov.uk/intellectual-property-mediation. If you cannot resolve the matter with the other party, then going to court may be the right solution. But it would be a good idea to seek legal advice at an early stage.