There are several good clinics in London, e.g. the neuro department at the Wellington hospital. BUT bring your money with you!!!!

p.s. Your symptoms are very typical following head injury. Sounds like what we call a foot drop and perhaps some flexion contracture/spasticity in the hand/wrist due to poor extensor recruitment. 4 years in there is hope for some change but that will be slow and take a long time with regular practice of the specific exercises that are prescribed. I just mention this as gaining anything may require yrs, not weeks, of dedication from you.

You might also look at a SAFO for your foot drop (Silicon Ankle Foot Orthosis). These provide a more natural support than a rigid AFO.