Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 106. Conditions for Prisoner-of-War Status
Section B. Levée en masse
The UK Military Manual (1958) considers that participants in a levée en masse
are recognised as being entitled to the privileges of belligerent forces if they fulfil the last two conditions laid down for irregulars, namely, if they carry arms openly and conduct their operations in accordance with the laws and customs of war. They are exempt from the obligations of being under the command of a responsible commander and wearing a distinctive sign. The inhabitants of a territory already invaded by the enemy who rise in arms do not enjoy the privileges of belligerent forces and are not entitled to be treated as prisoners of war, unless they are members of organised resistance movements fulfilling the conditions set out in the P.O.W. Convention, Art. 4A(2). 
United Kingdom, The Law of War on Land being Part III of the Manual of Military Law, The War Office, HMSO, 1958, § 97; see also 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 3, pp. 8–9, § 1(c).
The UK LOAC Manual (2004) states:
A levée en masse occurs where the “inhabitants of a territory not under occupation … on the approach of the enemy, spontaneously take up arms to resist the invading troops without having had time to organize themselves …” These inhabitants are treated as combatants provided that they carry arms openly and respect the laws and customs of war. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 4.8.
The UK LOAC Manual (2004), as amended in 2010, states that “when they [members of the civilian population] take part in the exceptional circumstances of a levée en masse, they … lose their civilian status, become combatants and are entitled to prisoner of war status.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, as amended by Amendment 3, Ministry of Defence, September 2010, § 4.2.2.