Dementia patients are entitled to a full diagnosis and treatment

My dad, Brian Webb is a 75 year old dementia patient who has been in severe pain since May. Stepping Hill hospital are trying to say that his pain is due to his dementia (all in his head). However, my family and I know when he is in real pain. All we want is a diagnosis and the relevant treatment! It is not too much to ask for a man who has paid into the NHS all his life, is it? It's my father's birthday on the 19th of December, with your help my father may be pain free for his birthday! Thanks so much.