There is, of course, some overlap here with some of the departments featured under 'Alternatives within law', and you do see legal jobs within the government advertised via the civil service online job search, but this entry is concerned with the non-legal aspect of civil service recruitment. Lawyers whose first priority is to assist with the running of the country via public sector work may find applying in a legal capacity via the Government Legal Service / Treasury Solicitors Office provides a more narrowed field of candidates. The potential for movement within government work is a well promoted feature.
There are 23 main Whitehall departments and 66 executive agencies comprising the umbrella network which confers services to the citizen through thousands of sub-outlets. Civil servants are the administrators and policymakers, of a huge diversity of specialisms, who implement services to the user. Management of health, schools, immigration, police, judicial system, agriculture, industry, armed forces, job-seekers, taxation, infrastructure, UK abroad, to policy matters regarding climate change, counter-terrorism, global economics.
The 'Senior Civil Service' exists to provide 'high-level' support to the government, and employs a broad group of some 3,900 experienced professionals in areas of finance, HR, procurement, legal, science and medicine, operational/project management, in 55 government departments and agencies across the country.
The Civil Service website advertises vacancies at www.civilservice.gov.uk/jobs, where you can register for email updates, search their database etc. The government legal service departments also advertise vacancies here, so you will see CPS, SFO etc lawyer ads. Details of Fast Steam entry are found at https://www.faststream.gov.uk/. There is also no age limit when applying to the Fast Stream, although it's a fairly rigorous process of testing and, much like completing a training contract in a law firm, the department you end up in will depend on available opportunities as much as your own preferences.