Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Related to Rule 94. Slavery and Slave Trade
The UK LOAC Manual (2004) states in its chapter on internal armed conflict that “outrages upon personal dignity … such as … slavery” are prohibited. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 15.30 and 15.30.4.
In its discussion on the 1977 Additional Protocol II, the manual specifies:
The following acts against protected persons, “are and shall remain prohibited at any time and in any place whatsoever”. These are:
f) slavery and the slave trade in all their forms. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.38(f).
Under the UK ICC Act (2001), it is a punishable offence to commit a crime against humanity as defined in Article 7(1)(c) of the 1998 ICC Statute, and war crimes as defined in Article 8(2)(b)(xxii) and (e)(vi) of the Statute. 
United Kingdom, ICC Act, 2001, Sections 50(1) and 51(1) (England and Wales) and Section 58(1) (Northern Ireland).
The UK Government Strategy on the Protection of Civilians in Armed Conflict (2010) states: “IHL requires parties to a conflict to respect and protect civilians. … [C]ivilians must not be … subjected to acts of violence such as … slavery”. 
United Kingdom, Foreign and Commonwealth Office, Government Strategy on the Protection of Civilians in Armed Conflict, March 2010, p. 4.