In 2025, there were approximately 181,000 personnel in the armed forces of the United Kingdom, 109,170 of which were in the British Army, 37,900 in the Royal Navy and 34,830 in the Royal Air Force. Regular personnel at historical lows in 2025 Overall, there has been a long-term decline in the size of the armed forces, with the number of personnel declining from over 200,000 in 2000, to around 137,000 by 2025. In fact, the size of the armed forces has been in almost constant decline since the end of the Second World War. Britain's retreat from its colonial empire throughout this period removed many of the UK's overseas commitments, with the end of the Cold War also leading to further cuts to personnel. This has also corresponded with cuts in defence spending, which fell from 4.6 percent of GDP in the mid-1980s, to just 1.8 percent in the late 2010s Operational deaths since the Second World War Since 1945, there have been 7,193 operational deaths in the United Kingdom’s armed forces, with the deadliest year occurring in 1951 when there were 851 deaths. This was due to three separate conflicts: the Malayan Emergency, the 1951 Anglo-Egyptian War and the Korean War. Since 1959, there were only three years that had more than 100 operational deaths: 1972, 1973 and 1982. By comparison, between 2016 and 2024, there have been only nine operational deaths, with just one death reported since 2023.

In April 2024, 13.1% of people in non-officer roles in the armed forces were from ethnic minorities, compared with 7.9% in April 2012.

In 2025, there were around 137,000 regular personnel serving in the British Armed Forces, compared with 138,000 in the previous year. In the first half of the twentieth century, there were two huge spikes in the number of active personnel which represented the final years of World War One and World War Two, numbering 4.58 million and 4.69 million in 1918 and 1945 respectively. Ever since 1945, the size of the regular armed forces has been in almost constant decline, with the noticeable exception of the early 1950s, when the number of active personnel increased by almost 200,000 because of the Korean War. The winds of change There are several reasons why the number of personnel in Britain’s armed forces has declined. Britain is involved in a far fewer conventional military conflicts today than it was in the past. As the size of Britain’s empire declined rapidly after 1945, so too did the UK's global military commitments. There are also more recent developments, such as the UK government’s Strategic Defence and Security Review of 2010, which outlined personnel would be cut throughout the 2010s to modernize the UK’s armed forces. Recent geopolitical events such as the War in Ukraine have, however, led to commitments from the UK government to spend more on defence, and eventually even a reversal of personnel cuts. Branches of the UK military There are three main branches of the UK armed forces, the British Army, the Royal Navy, the Royal Air Force, and the Royal Marines. Of the 181,000 people serving in the UK’s armed forces in 2025, over half of them were in the British Army, which had around 109,000 personnel. The next largest branch was the Royal Navy at 37,900, followed by the RAF at 34,800 personnel. The average age for people serving in the armed forces was 31 in 2024, with the Royal Air Force having a slightly higher average age group than the other branches, at 33.