Other sources of assistance include:
Royal Marines Charities and the Royal Naval Benevolent Fund (RM are part of the Naval Service).
For professional PTSD assistance, he should be referred to Combat Stress, who now have a contract with the MOD to provide PTSD assistance to SP and ex SP: They have a 24 hour helpline:
About us | Combat Stress
On the matter of the conduct of the Police, he should refer the matter to the Independent Police Complaints Commission:
Independent Police Complaints Commission