"My info may be out of date but back in the naughties I was instrumental in developing the regulatory process and documentation. Red Freds operated under BPA (British Parachute Association) rules. Their kit was all non military. I am not sure if they ever jumped "legally" from a service aircraft. Had they had an accident I am not sure if they ever addressed the "duty" issues. I am not saying that they were unprofessional."
Correct - they will jump from anything approved and available under BPA.