Well, shoot! What about flexeril or soma or Sklexan? Those are three different muscle relaxants that might ease the tension? Also the fentanyl patch is different than the morphine patch so maybe that would be worth a go.
Are you still taking the neurontin too? I would ask about celebrex or bextra or vioxx if they are available in the UK. That might help to get some of the inflammation down and help with pain.
I wish you could find something that would make you comfortable. I think if they cannot get you comfortable then they should admit you so they can figure out what works. Maybe an epidural to help knock the pain out?