On 24 August 1939, following the announcement of the Nazi–Soviet Pact the previous day, the House of Commons was recalled from its summer recess to pass the Emergency Powers (Defence) Bill, which gave authority to implement the Defence Regulations. The Act was originally intended to be in force for only one year, and made general provision for prosecuting the war effort. In particular, it provided for the following:

1. (1) Subject to the provisions of this section, His Majesty may by Order in Council make such Regulations (in this Act referred to as "Defence Regulations") as appear to him to be necessary or expedient for securing the public safety, the defence of the realm, the maintenance of public order and the efficient prosecution of any war [in which] His Majesty may be engaged, and for maintaining supplies and services essential to the life of the community.

(2) Without prejudice to the generality of the powers conferred by the preceding subsection, Defence Regulations may, so far as appears to His Majesty in Council to be necessary or expedient for any of the purposes mentioned in that subsection:-

(a) Make provision for the apprehension, trial, and punishment of persons offending against the Regulations and for the detention of persons whose detention appears to the Secretary of State to be expedient in the interests of the public safety or the defence of the realm;

(b) authorise -

(i) the taking of possession or control, on behalf of His Majesty, of any property or undertaking;

(ii) the acquisition, on behalf of His Majesty, of any property other than land;

(c) authorise the entering and searching of any premises; and

(d) provide for amending any enactment, for suspending the operation of any enactment, and for applying any enactment with or without modification.

[...]

(5) Nothing in this section shall authorise the imposition of any form of compulsory naval, military or air force service or any form of industrial conscription, or the making of provision for the trial by courts martial of persons not being persons subject to the Naval Discipline Act, to military law or to the Air Force Act.

The bill completed all its parliamentary stages, including royal assent, on that day.^[2] The question of compensation was not directly addressed by the bill, but the subsequent Compensation (Defence) Act 1939 (2 & 3 Geo. 6. c. 75) established a statutory compensation scheme in respect of land, vessels, vehicles, aircraft and other property a week later.^[3]

The Defence Regulations were Orders in Council and could amend any primary or secondary legislation within the limits of the enabling Acts to allow the effective prosecution of the war.

The regulations existed in draft form, constantly revised, throughout the years between the world wars.^[4] In early 1939 it was decided that since a war might break out without warning or without time to pass an act of Parliament to bring in emergency regulations, the regulations should be split into two codes. Code A would be needed immediately if war broke out and could be passed in peacetime, while Code B, containing more severe restrictions on civil liberties, would be brought in later. In order not to alert the public to the existence of Code B, Code A was simply numbered consecutively.^[5]

The main Defence Regulations were the Defence (General) Regulations 1939 (SR&O 1939/927), which implemented Code A and were brought into effect immediately.^[6] Code B followed on 1 September (the same day Nazi Germany invaded Poland) in the form of the Defence (General) Regulations (Miscellaneous Amendments) Order 1939 (SR&O 1939/978) and included Defence Regulation 18B, which provided a framework for internment.^[6] The 1939 regulations were amended dozens of times throughout the war, including by the Defence (General) Regulations (Miscellaneous Amendments) Order 1939 (SR&O 1939/1681), Defence (General) Regulations (Amendment) Regulations 1940 (SR&O 1940/1134)^{[citation needed]}, in 1941 (adding Regulation 78^[7]) and in 1945 (adding Regulation 69D^[8]). By May 1945, some 377 Defence (General) Regulations had been created.^[9]

Other Defence Regulations covered narrower fields of life such as the Defence (Finance) Regulations 1939 (SR&O 1939/1620), the Defence (Armed Forces) Regulations 1939 (SR&O 1939/1304), Defence (Administration of Justice) Regulations 1940 (SR&O 1940/1028), Defence (Summer Time) Regulations 1939 (SR&O 1939/1379) and Defence (Trading with the Enemy) Regulations 1940 (SR&O 1940/1092). Some Regulations included powers for a minister to make further provision by way of orders.

Taken together, the Defence Regulations provided the legal basis for a number of measures aimed at the Home Front including the establishment of the Home Guard, the institution of rationing, and nighttime blackouts.^[10]

The Emergency Powers (Defence) Act 1940 (3 & 4 Geo. 6. c. 20) extended the 1939 Act for another year, and provided for annual extensions by parliamentary resolution.^[11] It also extended the government's powers under the Defence Regulations to require persons "to place themselves, their services and their property at the disposal of His Majesty" though the practical significance of this extension is unclear given the Government had already passed the National Service (Armed Forces) Act 1939 and the Control of Employment Act 1939 (2 & 3 Geo. 6. c. 104).^[11]

Originally the regulations did not create any capital offences, since the law of treason was thought to be sufficient. Defence Regulation 2A provided that "If, with intent to assist the enemy, any person does any act which is likely to assist the enemy or to prejudice the public safety, the defence of the realm or the efficient prosecution of the war, he shall be liable to penal servitude for life."^[12]

However, in 1940 amendments to the regulations created two capital offences: "forcing safeguards" (breaking through roadblocks etc.) under regulation 1B, and looting under regulation 38A.^[1] A third new capital offence, called treachery, was created soon afterwards by the Treachery Act 1940.

The Emergency Powers (Defence) (No. 2) Act 1940 (3 & 4 Geo. 6. c. 45) enabled the creation of special courts to administer criminal justice in war zones, as well as authorizing them to punish offenders for violating the Defence Regulations.^[13]

After the end of the war, the Defence Regulations were continued in force by the Supplies and Services (Transitional Powers) Act 1945 (9 & 10 Geo. 6. c. 10) and later by the Emergency Laws (Transitional Provisions) Act 1946 (9 & 10 Geo. 6. c. 26). They continued to be amended periodically, including by the Defence Regulations (No. 2) Order 1949 and the Defence Regulations (No. 3) Order 1949.^[14] Some were repealed, for example by the Land Powers (Defence) Act 1958.

The Emergency Laws (Repeal) Act 1959 (7 & 8 Eliz. 2. c. 19) repealed most of the Defence (General) Regulations, with the exception of:^[15]

• No. 55 (giving general power to control industry for wide purposes);
• No. 55AA (empowering the government to secure the necessary information for these purposes); and
• No. 55AB (giving power to impose price control of goods and services).

The 1959 Act also preserved Regulation 2A of the Defence (Finance) Regulations 1939 (power of Treasury to prohibit action on certain orders as to gold, etc.) and the Regulation 6 of the Defence (Armed Forces) Regulations 1939 (power to employ troops on agricultural or other urgent work of national importance).^[15] Under the terms of the 1959 Act, the last of the Defence Regulations were due to expire on 31 December 1964.^[16] However, Regulation 6 of the Defence (Armed Forces) Regulations 1939 was made permanent by the Emergency Powers Act 1964, and several of the other regulations were re-enacted on a permanent basis by the Emergency Laws (Re-enactments and Repeals) Act 1964 (c. 60). As of 2023, Regulation 6 (which authorises the use of service personnel to perform agricultural and other "urgent work of national importance") remains in force.

• Defence of the Realm Act 1914
• Emergency Powers Act 1920
• Capital punishment in the United Kingdom

• Balogh, T. (28 August 1943). "Control over Property". Bulletin of the Oxford University Institute of Economics & Statistics. 5 (12): 196–199. doi:10.1111/j.1468-0084.1943.mp5012003.x. ISSN 0140-5543.
• Cotter, Cornelius P. (1953). "Constitutionalizing Emergency Powers: The British Experience". Stanford Law Review. 5 (3): 382–417. doi:10.2307/1226448. JSTOR 1226448.
• Jennings, W. Ivor (1940). "The Emergency Powers (Defence) (No. 2) Act, 1940". Modern Law Review. 4 (2): 132–136. doi:10.1111/j.1468-2230.1940.tb02739.x. JSTOR 1090251.
• Leeson, David (2012). "Emergency Powers Acts (1920, 1926, 1939–1940, 1964)". In Martel, Gordon (ed.). The Encyclopedia of War. Wiley-Blackwell. ISBN 978-1-40519037-4.
• Simpson, Alfred William Brian (1994). In the Highest Degree Odious: Detention Without Trial in Wartime Britain. Oxford University Press. pp. 43–50. ISBN 978-0-19-825949-7.

• Full text of the Emergency Powers (Defence) Act 1939, as included in Le May, G. (1955). British Government, 1914–1953: Select Documents. London: Meuthen And Co London.
• Full text of the Emergency Powers (Defence) Act 1940, as included in Le May, G. (1955). British Government, 1914–1953: Select Documents. London: Meuthen And Co London.
• Full text of the Compensation (Defence) Act 1939 from legislation.gov.uk.
• Full text of the Emergency Laws (Repeal) Act 1959 from legislation.gov.uk.