Many NHS hospitals have private wards where private patients may use the accommodation and services of the hospital provider. Some hospitals also provide amenity beds, usually located in small side wards for which a charge is made for the accommodation. Both of these categories of patient are defined by the NHS Act of 1977. Any categories of patient, whether NHS, private or amenity patients, can be formally detained under the provisions of the Mental Health Act 1983 and other legislation.

Most patients in NHS hospitals or hospital units will come under category 10 (see below).

10 = NHS patient: not formally detained

11 = NHS patient: formally detained under Part II of the Mental Health Act 1983

12 = NHS patient: formally detained under Part III of the Mental Health Act 1983 or under other Acts

13 = NHS patient: formally detained under part X, Mental Health Act 1983*

20 = Private patient: not formally detained

21 = Private patient: formally detained under Part II of the Mental Health Act 1983

22 = Private patient: formally detained under Part III of the Mental Health Act 1983 or under other Acts

23 = Private patient: formally detained under part X, Mental health Act 1983*

30 = Amenity patient: not formally detained

31 = Amenity patient: formally detained under Part II of the Mental Health Act 1983

32 = Amenity patient: formally detained under Part III of the Mental Health Act 1983 or under other Acts

33 = Amenity patient: formally detained under part X, Mental health Act 1983*

null = Other maternity event.

* Codes 13, 23 and 33 were introduced at the start of the 1994-95 HES year (1 April 2025)