MG,
Having recovered from 3 serious mtb injuries which all required surgery I feel your pain.
My advice would be to keep with your private physio who understands your needs and will accelerate your rehab as much as you can tolerate and is safe for your injury. NHS physios are fantastic however are functioning in a system where they are unable to deliver appropriate levels of care. Its not their fault.
I would also recommend that you get clear instructions on what you exercises you can do in your own time and what limits you can push yourself.
I’ve had excellent results from all my injuries which were severe but I became completely obsessed with them.
I broke and dislocated my shoulder and had reconstruction surgery.
Before your bone has healed enough you need to perform ppassive exercises – ie not under your own power.
When the bone has healed enough you can increase this to asssisted active and then fully active exercises.
There are many simple ways you can do your own physio at home or in your office daily – I did this multiple times per day.
It would be innappropriate for me to recommend things for you here, but I highly recommend that you get this advice from your private physio.
Good luck mate I will watch this thread with interest.