Main entrance sign to Northwick Park and St. Mark's Hospitals, London, UK. Northwick Park Hospital is a large hospital located in North West London. It is primarily a National Health Service hospital although there are some private funding units. St. Mark's Hospital was founded in 1835 by Frederick Salmon to treat patients with anorectal disorders. St. Mark's hospital is both a national and international referral centre for intestinal and colorectal disorders as well as researching and running a programme devised to teach and educate about the diseases.