The MOD states that its principal objectives are to defend the United Kingdom of Great Britain and Northern Ireland and its interests and to strengthen international peace and stability.

The formation of a united ministry of defence was rejected by the coalition government of David Lloyd George in 1921, but the Chiefs of Staff Committee was formed in 1923, for the purposes of inter-service co-ordination.

[7] The unification of all defence activities under a single ministry was motivated by a desire to curb interservice rivalries and followed the precedent set by the American National Security Act of 1947.

Police claimed he received at least £3.5m in total in corrupt payments, such as substantial bribes from overseas arms contractors aiming to influence the allocation of contracts.

This was confirmed by Sue Ellison, a representative of the Defence Science and Technology Laboratory at Porton Down who said that the results from these trials "will save lives, should the country or our forces face an attack by chemical and biological weapons."

In February 2019, former soldier Inoke Momonakaya won £458,000 payout after a legal battle for the racial harassment and bullying he received while serving in the army.

[11] In August 2019, A Commons Defence Select Committee report revealed that several female and BAME military staff have raised concerns regarding discrimination, bullying and harassment.

[12] In September 2019, two former British army soldiers Nkululeko Zulu and Hani Gue won a racial discrimination claim against the Ministry of Defence (MoD).

[13] In November 2019, mixed race soldier Mark De Kretser sued MoD for £100k claiming he was subjected to "grindingly repetitive" racist taunts from colleagues.

Its members train on weekly evenings and monthly weekends, as well as two-week exercises generally annually and occasionally bi-annually for troops doing other courses.

[17] Specific examples of overspending include: In May 2024, the ministry's payroll system was reportedly targeted multiple times in a cyberattack in which personnel and their bank details were compromised.

[31] The role works closely with the Chief of the Defence Staff in leading the organisation and supporting Ministers in the conduct of business in the department across the full range of responsibilities.

[41] Competitive procurement processes are used whenever possible,[42] and all new direct tender and contract opportunities valued over £10,000 are advertised on a system called the Defence Sourcing Portal.

[47] The Ministry of Defence is one of the United Kingdom's largest landowners, owning 227,300 hectares of land and foreshore (either freehold or leasehold) at April 2014, which was valued at "about £20 billion".

[48] The defence estate is divided as training areas & ranges (84.0%), research & development (5.4%), airfields (3.4%), barracks & camps (2.5%), storage & supply depots (1.6%), and other (3.0%).