Dear Mr. Hollingsworth,
You might be suffering from one of inflammatory spinal disease
(like ankh losing spondylitis, please google it).
Have you done HLA B-27 test? Usually positive in ankylosing spondylitis
Consult a spine doctor in your area, they can tell whether you have it or not by looking at your x ray.
Treatment is mostly with physiotherapy
Also, a rheumatologist
might give you some medications to reduce the inflammation and pain.
It's difficult to improve flexibility, but you can try to save whatever is left by physio.
Hope this helps,
Dr. Amit Sharma