Gwenny. I'm not sure entirely how NHS works up there. But you asked who was in control. YOU ARE! And you must take that stance if you want the proper treatment.
It sounRAB like your family doc is trying to play super doc and wants to be what I call a Maverick and solve all your problems even if she's not specialized enough to do so.
If I were in your shoes and the ability was available to me, I would change doctors now rather than later. If she's not listening to you now.. what happens down the road when or if you get worse? She's doing what she wants without any consult and agreement with you. There MUST be teamwork between you and any doctor you see, especially when it comes to sleuthing out this back crap.
Keep the appointment to get the MRI done. But when you are in there.. ask them to provide YOU with a copy of the report. They may not give you the films, but they should be able to provide you with a "copy" of the written report of what the radiologist sees on the MRI that will be done. And keep them going forward. It will help you if you need to change doctors and then dont have to wait to obtain that record.
This kind of treatment even happens with the surgeons as well. I had one that did nothing but medicate me and send me to therapy for over 2 years. She should have been running more tests over that time to try and find the source of my pain, but she didnt and I suffered needlessly, but I sat back and just did what she told me, not really involved like I should have been to begin with. After this, I learned to take charge of health and advocate for myself, and searched for the right spine surgeon to help me. I found him!
I hope this helps you some and please let us know what you find out with the MRI. If you can continue with the Physio.. do. Keeping up with as much of it as you possibly can is going to help you in the long run.