In the United Kingdom, the Civil Service is the permanent bureaucracy or secretariat of Crown employees which supports His Majesty's Government (as well as the devolved Scottish Government and Welsh Government – the Northern Ireland Civil Service being a separate civil service), which is led by a cabinet of ministers chosen by the Prime Minister of the United Kingdom of Great Britain and Northern Ireland.

As in other states that employ the Westminster political system, the Civil Service – often known by the metonym of Whitehall – forms an inseparable part of the British government. The executive decisions of government ministers are implemented by the Civil Service. Civil servants are employees of the Crown and not of the British parliament. Civil servants also have some traditional and statutory responsibilities which to some extent protect them from being used for the political advantage of the party in power. Senior civil servants may be called to account to Parliament.

In general use, the term civil servant in the United Kingdom does not include all public sector employees. Although there is no fixed legal definition, the term is usually defined as a "servant of the Crown working in a civil capacity who is not the holder of a political (or judicial) office; the holder of certain other offices in respect of whose tenure of office special provision has been made; [or] a servant of the Crown in a personal capacity paid from the Civil List". As such, the civil service does not include government ministers (who are politically appointed); members of the British Armed Forces; police officers; officers of local government authorities; employees of some non-departmental public bodies; officers or staff of either of the Houses of Parliament; employees of the National Health Service (NHS); or staff of the Royal Household. As of the end of March 2021 there were 484,880 civil servants in the Civil Service, an increase of 6.23 per cent on the previous year.

the incorruptible spinal column of England

— John Gunther, 1940

The Offices of State grew in England, and later the United Kingdom centred around the street Whitehall, hence the metonym. Initially, they were little more than secretariats for their leaders, who held positions at court. They were chosen by the king on the advice of a patron, and typically replaced when their patron lost influence. In the 18th century, in response to the growth of the British Empire and economic changes, institutions such as the Office of Works and the Navy Board grew large. Each had its own system and staff were appointed by purchase or patronage. By the 19th century, it became increasingly clear that these arrangements were not working.

Under Charles Grant, the East India Company established the East India Company College at Haileybury near London, to train administrators, in 1806. The college was established on recommendation of officials in China who had seen the imperial examination system. In government, a civil service, replacing patronage with examination, similar to the Chinese system, was advocated a number of times over the next several decades.

William Ewart Gladstone, in 1850, an opposition member, sought a more efficient system based on expertise rather than favouritism. The East India Company provided a model for Stafford Northcote, private Secretary to Gladstone who, with Charles Trevelyan, drafted the key report in 1854. The Northcote–Trevelyan Report recommended a permanent, unified, politically neutral civil service, with appointments made on merit, and a clear division between staff responsible for routine ("mechanical") and those engaged in policy formulation and implementation ("administrative") work. The report was not implemented, but it came as the bureaucratic chaos in the Crimean War demonstrated that the military was as backward as the civil service. A Civil Service Commission was set up in 1855 to oversee open recruitment and end patronage as Parliament passed an Act "to relieve the East India Company from the obligation to maintain the College at Haileybury". Prime Minister Gladstone took the decisive step in 1870 with his Order in Council to implement the Northcote-Trevelyan proposals. This system was broadly endorsed by commissions chaired by Playfair (1874), Ridley (1886), MacDonnell (1914), Tomlin (1931) and Priestley (1955).