Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 35. Hospital and Safety Zones and Neutralized Zones
The UK Military Manual (1958) provides for the possibility of establishing, by agreement between the parties before or after the outbreak of hostilities, hospital and safety zones and localities, either in occupied territory or in the territory of a belligerent. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, §§ 26 and 363.
The manual further allows any belligerent to propose to the opposing belligerent, either directly or through a neutral State or a humanitarian organization, the establishment of neutralized zones in the area of combat, “to shelter from the effects of war wounded or sick combatants or non-combatants and civilian persons who take no part in the hostilities and who perform no work of a military character”. 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 27.
The UK LOAC Pamphlet (1981) provides that “safety zones may be set up to contain hospitals, shelters for the wounded and sick, the old and infirm, children under 15 years of age, expectant mothers and mothers with children under 7 years of age”. 
United Kingdom, The Law of Armed Conflict, D/DAT/13/35/66, Army Code 71130 (Revised 1981), Ministry of Defence, prepared under the Direction of The Chief of the General Staff, 1981, Section 9, p. 34, § 2.
The UK LOAC Manual (2004) states:
5.40. Neutralized zones may be established in regions where fighting is taking place to shelter the wounded and sick, whether combatants or non-combatants, and civilians from the effects of war.
5.40.1. These civilians may not perform work of a military character while they reside in the zone. For the purpose of establishing such zones, the written agreement of the parties to the conflict is required. That agreement may be reached either directly or through a neutral state or humanitarian organization. The agreement must define the location and area of the zone, its commencement and duration and also the arrangements for its administration, food supply and supervision. A neutralized zone is likely to be established in an area where the fighting is taking place. It is likely to be a very limited area and its purpose is very limited. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.40–5.40.1.
The manual further states:
5.41. Hospital and safety zones and localities may be established in peacetime or in time of armed conflict and in occupied territory “to protect from the effects of war, wounded, sick and aged persons, children under fifteen, expectant mothers and mothers of children under seven.”
5.41.1. After the outbreak of hostilities, the parties to the conflict may conclude agreements on the mutual recognition of these zones. The agreement may be modelled on the draft annexed to Geneva Convention IV. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.41–5.41.1.
In addition, the manual states:
The Geneva Conventions and Additional Protocol I recognize that, on a number of matters, agreements between belligerents may be desirable or necessary. These cover such matters as … agreements as to the location and marking of hospitals and demilitarized zones. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 10.39.
In its chapter on air operations, the manual states that “attacks on non-defended localities and zones under special protection are prohibited”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 12.26.
In its chapter on maritime warfare, the manual provides: “The parties to the conflict may agree, for humanitarian purposes, to create a zone in a defined area of the sea in which only activities consistent with those humanitarian purposes are permitted.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 13.114.
Lastly, with regard to internal armed conflict, the manual provides that (in addition to the prohibition of attacks on undefended localities) “[t]he other rules on protective zones applicable in international armed conflicts may be applied by analogy to internal armed conflicts”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.25.2.
During the war in the South Atlantic, at the United Kingdom’s suggestion, and without any special agreement in writing, the parties to the conflict established a neutral zone at sea. This zone, called the Red Cross Box, with a diameter of approximately 20 nautical miles, was located on the high seas to the north of the islands. Without hampering military operations, it enabled hospital ships to hold position and exchange British and Argentine wounded. 
Sylvie S. Junod, Protection of the Victims of Armed Conflict: Falkland-Malvinas Islands (1982): International Humanitarian Law and Humanitarian Action, ICRC, Geneva, 2nd edition, December 1985, pp. 23–24, and 26.