Question: When did the inspiration of Supermac service as Prime Minister of the United Kingdom?

Context paragraphs:
Luis González-Bravo y López de Arjona: Luis González Bravo y López de Arjona (Cádiz, Spain, 8 July 1811 – Biarritz, France, 1 September 1871) was a Spanish politician, diplomat, intellectual, speaker, author, philanthropist and journalist graduated from law school, who served twice as Prime Minister of Spain, or President of the Government of Spain (Spanish terminology for Prime Minister), from 1843 to 1844 and in 1868.  He held other important offices, such as once serving as Minister of State and Foreign Affairs, and twice as Minister of Home Affairs (see: List of Ministers of the Interior of Spain).  He was appointed Ambassador of Spain to the United Kingdom in Queen Victoria's rule, and Ambassador of Spain to Portugal.  He was the Spanish Prime Minister responsible for granting Chile its independence.  He was a member of the Moderate Party, and occupied three times the post of Spanish Congressman (United States House of Representatives equivalent) or Member of Parliament (House of Commons of the United Kingdom equivalent), for Cádiz, Jaén, and the Canary Islands.  He was provisional Minister of Justice for five days.  He was head of the Spanish civil troops "Milicia Nacional".  He was Knight of the Order of the Golden Fleece and Knight of the Order of Charles III (of King Charles III of Spain, Carlos III).  He founded four newspapers in Spain, and was the noted Spanish poet Gustavo Adolfo Bécquer's benefactor.

Prime Minister of Northern Ireland: The Prime Minister of Northern Ireland was the head of the Government of Northern Ireland between 1921 and 1972.  No such office was provided for in the Government of Ireland Act 1920, however the Lord Lieutenant, as with Governors-General in other Westminster Systems such as in Canada, chose to appoint someone to head the executive even though no such post existed in statute law.  The office-holder assumed the title "Prime Minister" to draw parallels with the Prime Minister of the United Kingdom.  On the advice of the new Prime Minister, the Lord Lieutenant then created the "Department of the Prime Minister".  The office of Prime Minister of Northern Ireland was abolished in 1972, along with the contemporary government, when direct rule of Northern Ireland was transferred to London.

Prime Minister's Official Spokesperson: The Prime Minister's Official Spokesperson or alternatively Prime Minister's Official Spokesman/Spokeswoman is a position in the United Kingdom's Civil Service, located in the Prime Minister's Office in 10 Downing Street and used by the British Prime Minister to convey information to the public.  The Prime Minister's Official Spokesperson usually addresses a small group of press and media correspondents, known as lobby correspondents, each morning to deliver statements on current events on behalf of the Prime Minister.

Premiership of Gordon Brown: The premiership of Gordon Brown began on 27 June 2007 when Brown accepted the Queen's invitation to form a government, replacing Tony Blair as the Prime Minister of the United Kingdom.  It ended with his resignation as Prime Minister on 11 May 2010.  While serving as Prime Minister, Brown also served as the First Lord of the Treasury, the Minister for the Civil Service and the Leader of the Labour Party.  He was succeeded as Prime Minister by David Cameron

British-American Parliamentary Group: The British-American Parliamentary Group is a all-party parliamentary group consisting of members of the Parliament of the United Kingdom.  “The objects of the British-American Parliamentary Group are to promote friendly relations and mutual understanding between Members of both Houses of Parliament of the United Kingdom and Members of both Houses of Congress of the United States of America; to discuss problems common to the United Kingdom and the United States; to exchange courtesies and to provide opportunities for discussion with Senators, members of the House of Representatives, and other distinguished citizens of the United States; and to arrange for the exchange of visits and information between legislators of both countries.”  Its co-presidents are the Speaker of the House of Commons and the Lord Speaker, among the vice presidents are former Speakers of the House of Commons, one former prime minister, the current deputy prime minister, former leaders of the opposition, and former foreign secretaries.  The chairman is the prime minister.  There are currently over 600 members from both the Labour and Conservative parties.

Principal Private Secretary to the Prime Minister: The Principal Private Secretary to the Prime Minister is a senior official in the British Civil Service who acts as Principal Private Secretary to the Prime Minister of the United Kingdom.  The holder of this office is traditionally the head of the Prime Minister's Office.  In the Civil Service, the role is currently graded as a Director-General.  To date, no woman has ever occupied the office.  In fiction, the character of Bernard Woolley in the television series "Yes, Prime Minister", occupied this post.

Supermac (cartoon): "Super-Mac" was a 1958 cartoon image of Harold Macmillan, which became an enduring nickname for him.

Swedish governmental line of succession: The Swedish constitution of 1974 allows the Prime Minister of Sweden to appoint one of the Ministers in the cabinet as Deputy Prime Minister ("biträdande statsminister", also unofficially known as "vice statsminister", "Vice Prime Minister"), in case the Prime Minister for some reason is prevented from performing his or her duties.  However, if a Deputy Prime Minister has not been appointed, the Minister in the cabinet who has served the longest time (and if there are several with equal experience the one who is oldest) takes over as head of government.  Note that the person acting as Prime Minister does not do so on a permanent basis: if a Prime Minister dies, resigns or loses a vote of confidence in the Riksdag, the Speaker of the Riksdag will then confer with the parties of the Riksdag and propose a new Prime Minister, who must be tolerated by a majority of the Riksdag.  If the Prime Minister has resigned or lost a vote of confidence, he or she will remain the head of a government "ad interim" until the new Prime Minister assumes his or her office.  The only case where the governmental line of succession becomes relevant is when the Prime Minister dies (upon which the person next in the line of succession serves as the head of a government "ad interim") or when the Prime Minister is on leave or for any other reason incapable of serving, but still remains in office.  This might be compared to the Presidential line of succession in the United States, where the person next in line assumes the Presidency throughout the remainder of the term if the President dies, resigns or is impeached.

Harold Macmillan: Maurice Harold Macmillan, 1st Earl of Stockton, {'1': ", '2': ", '3': ", '4': "} (10 February 1894 – 29 December 1986) was a British statesman of the Conservative Party who served as Prime Minister of the United Kingdom from 1957 to 1963.  Nicknamed "Supermac", he was known for his pragmatism, wit and unflappability.

List of Prime Ministers of the United Kingdom: The Prime Minister of the United Kingdom is the head of the Government of the United Kingdom, and chairs Cabinet meetings.  There is no specific date when the office of Prime Minister first appeared, as the role was not created but rather evolved over a period of time.  The term was used in the House of Commons in 1805 and it was certainly in parliamentary use by the 1880s, and in 1905 the post of Prime Minister was officially given recognition in the order of precedence.  Modern historians generally consider Sir Robert Walpole, who led the government of Great Britain from 1721 to 1742, as the first Prime Minister.  Walpole is also the longest-serving Prime Minister by this definition.  However, Sir Henry Campbell-Bannerman was the first Prime Minister and Margaret Thatcher the longest-serving Prime Minister to have been officially referred to as such.

Supporting paragraphs: Supermac (cartoon) Harold Macmillan
Answer: 1957 to 1963