All laws here attempt (at best) to be 1:1 with the current UK laws, and your rights are included in that. As Drama put it, there are pressing circumstances that would give police the powers of search and seizure. Keep in mind that there are lot of police who know how to trick you into thinking they have the powers so you give consent without even realizing it.
The best thing you can do is simply claim "I do not consent to this search!" and alert them that you have a Go-Pro that is recording the situation. You may than raise the concern with the Police Complaints Commission and a senior officer will review the situation and take action if the situation was not pressing enough to warrant a search. To ensure you have all of the information, ask the officer what situation empowers them to search your vehicle and double-check it yourself. (Such as being 1km in the vicinity of a drug-related area.) You may find that claiming you are recording and will be speaking to their superiors will make the less sure officers leave you be.