Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 31. Humanitarian Relief Personnel
The UK LOAC Manual (2004) states:
Relief personnel may, where necessary, accompany relief consignments, “subject to the approval of the Party in whose territory they will carry out their duties”. They are entitled to respect and protection and parties are under an obligation to assist them “to the fullest extent practicable”. Only “imperative military necessity” can justify any limitation on their activities or restriction of movement, which must in any event be temporary. Relief personnel are under an obligation not to exceed the terms of their mandate under Additional Protocol I and to “take account” of the security requirements of the party in whose territory they are carrying out their duties. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 9.13.
With regard to internal armed conflict, the manual states:
15.27. It is prohibited to attack the “personnel, installations, material, units or vehicles involved in a humanitarian assistance or peacekeeping mission in accordance with the Charter of the United Nations, so long as they are entitled to the protection given to civilians or civilian objects under the international law of armed conflict”.
15.27.1. The protection and delivery of relief supplies will usually be dealt with in agreements between the state concerned and the relief agencies in question. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 15.27.–15.27.1.
The UK UN Personnel Act (1997), which gives effect to certain provisions of the 1994 Convention on the Safety of UN Personnel, provides:
If a person does outside the United Kingdom any act to or in relation to a UN worker which, if he had done it in any part of the United Kingdom, would have made him guilty of any of the offences mentioned in subsection (2) inter alia murder, manslaughter, culpable homicide, rape, assault causing injury, kidnapping, abduction and false imprisonment], he shall in that part of the United Kingdom be guilty of that offence. 
United Kingdom, UN Personnel Act, 1997, Section 1(1).
Under the UK ICC Act (2001), it is a punishable offence to commit a war crime as defined in Article 8(2)(b)(iii) and (e)(iii) of the 1998 ICC Statute. 
United Kingdom, ICC Act, 2001, Sections 50(1) and 51(1) (England and Wales) and Section 58(1) (Northern Ireland).
In 1992, during a debate in the UN Security Council on the situation in Bosnia and Herzegovina, the United Kingdom stated that attacks on ICRC personnel were contrary to all the provisions of IHL. 
United Kingdom, Statement before the UN Security Council, UN Doc. S/PV.3106, 13 August 1992, p. 36.
The Report on UK Practice states that “as regards protection of relief personnel and objects, the United Kingdom has, both in words and in action, demonstrated support for this principle, as in Iraq, and in the former Yugoslavia”. 
Report on UK Practice, 1997, Chapter 4.2.
In 2008, during a debate in the House of Commons, the UK Parliamentary Under-Secretary of State for International Development stated:
The [UK] Government welcome the commitment of the Government of Sri Lanka to protect civilian populations and have continued to lobby for all parties in the conflict to respect their obligations under international humanitarian law. Those include the protection of … humanitarian workers. 
United Kingdom, House of Commons, Statement by the Parliamentary Under-Secretary of State for International Development, Hansard, 14 October 2008, Vol. 704, Westminster Hall, col. 246 WH.