Following economic chaos, democratic government has been overthrown in a bloodless coup, the Royal Family fled into self-imposed exile and England is ruled autocratically by Prime Minister Sir Timothy Hobson.

Each episode begins with a column of Guardians marching through central London to a memorable theme tune composed by Wilfred Josephs.

The dominant group within Quarmby favours a strategy of provoking increased oppression by the state through the use of assassination and other forms of terrorism.

Hobson represents the liberal element within government, attempting to outmanoeuvre the seldom-seen General and the polished Cabinet Secretary Norman.

The series was originally broadcast between 10 July 1971 and 2 October 1971 on all ITV stations with the exception of Ulster Television (UTV); since UTV served the Northern Ireland area, which was in the early stages of the Troubles, the Independent Television Authority decided that the series was unsuitable for broadcast there due to its political content such as depictions of terrorist activity from the terrorist's point of view, and due to a desire to avoid any unintended connection to the Republic of Ireland's Garda Síochána (whose name translates into "Guardians of the Peace", while the full name of the titular Guardians organisation is "Guardians of the Realm").