Physio and ost can only treat certain conditions. If the pain is severe, and i mean proper severe not shandy drinking southern severe then the GP will eventually refer you to a specialist. You may then be granted a MRI scan. This is the only way to truly diagnose the issue. I know this from personal experience after having spinal surgery. Good luck. In my experience it is the NHS physio who will gatekeep any onward referral. When my back was at its worst it was gp for anti-inflammatory medicine, physio as expert in musculoskeletal health, it was looking like we might have needed to look towards surgery (luckily not because I actually did my exercises) and it would have been the physio who directed that referral. In the three counties I have accessed back healthcare in the past ten years this very good example of stepped care has been folllowed. Best tip is do not dismiss the idea of the exercises from the Physioterrorist, even with backs that feel debilitating and very painful the right exercises can be the solution and. Surgery almost never (in my experience with family and peers) lead to solving the problem just diminishing the impact a bit. Life of bad back is feasible with surgery.