Question: in what position did Mark Beresford Russell Grant-Sturgis serve under the person who would later be the prime minister of the united kingdom?

Context articles: List of Prime Ministers of the United Kingdom
Shadow First Secretary of State
H. H. Asquith
Swedish governmental line of succession
Deputy Prime Minister (Greenland)
Mark Beresford Russell Grant-Sturgis
Prime Minister of Northern Ireland
Beresford-Peirse baronets
Prime Minister's Official Spokesperson
Later life of Winston Churchill

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.
The Shadow First Secretary of State is a position in the United Kingdom's Shadow Cabinet that was created on 11 May 2015 by the Leader of the Opposition, Harriet Harman for her interim shadow cabinet.
 Prior to 2015, the office was known as Shadow Deputy Prime Minister of the United Kingdom.
 Even though the role has no specific responsibilities attached to it, the holder of the position shadows the First Secretary of State and deputises for the Leader of the Opposition in Prime Minister's Questions when the First Secretary is deputising for the Prime Minister.
 The current holder is Emily Thornberry who was appointed on 14 June 2017.
Herbert Henry Asquith, 1st Earl of Oxford and Asquith, (12 September 1852 – 15 February 1928), generally known as H. H. Asquith, served as the Liberal Prime Minister of the United Kingdom from 1908 to 1916, and was the last Liberal leader to lead that party in government without forming a coalition.
 He had a central role in the design and passage of major liberal legislation.
 In August 1914, Asquith took the United Kingdom into the First World War, but resigned amid political conflict in December 1916 and was succeeded by his War Secretary David Lloyd George.
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.
Deputy Prime Minister of Greenland is a position, held by one government minister, in the Government of Greenland who can take the position of acting Prime Minister when the Prime minister is temporarily absent.
 The job is unofficial, but in many media, the person taking over when the Prime Minister is absent, is often dubbed Deputy Prime Minister, or Naalakkersuisut siulittaasuata tullia in Greenlandic.
Sir Mark Beresford Russell Grant-Sturgis KCB (1884–1949) was Assistant Under-Secretary for Ireland.
 The son of Julian Sturgis and Mary Maud Sturgis "née" Beresford, he was educated at Eton College before becoming assistant private secretary to then chancellor of the exchequer, H. H. Asquith.
 He married Ellen Rachel Montagu-Stuarty-Wortley on July 9, 1914.
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.
The Beresford, later Beresford-Peirse Baronetcy, of Bagnall in the County of Waterford, is a title in the Baronetage of the United Kingdom.
 It was created on 21 May 1814 for John Beresford.
 He was an admiral in the Royal Navy and also represented Coleraine, Berwick-on-Tweed, Northallerton and Chatham in the House of Commons.
 Beresford was the illegitimate son of George Beresford, 1st Marquess of Waterford, and the brother of William Beresford, 1st Viscount Beresford.
 He was succeeded by his son, the second Baronet, from his first marriage to Mary Molloy.
 He died without surviving male issue and was succeeded by his nephew, the third Baronet.
 He was the eldest son of Henry William de la Poer Beresford-Peirse (1820–1859), eldest son of the first Baronet's second marriage to Harriett Elizabeth, daughter of Henry Peirse.
 He served as Chairman of the North Riding of Yorkshire County Council.
 His grandson, the fifth Baronet, was Director-General of the Forestry Commission between 1962 and 1968.
 As of 2014 the title is held by the latter's grandson, the seventh Baronet, who succeeded his father in 2013.
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.
The later life of Winston Churchill documents the life of the British statesman from the end of World War II and his second term as Prime Minister of the United Kingdom, until his subsequent death and funeral in 1965.
 After the end of the war Churchill had to step down as Prime Minister of the United Kingdom because the Conservative Party lost the 1945 election.
 For six years he was to serve as the Leader of the Opposition.
 During these years Churchill continued to influence world affairs; in 1946 he gave his Iron Curtain speech which spoke of the expansionist policies of the USSR and the creation of the Eastern Bloc; Churchill also argued strongly for British independence from the European Coal and Steel Community (which he saw as a Franco-German project as Britain still had an empire).
 In the General Election of 1951 Labour was defeated and Churchill became Prime Minister for a second time.
 Churchill continued to lead Britain but was to suffer increasingly from health problems.
 Aware that he was slowing down both physically and mentally he resigned from the Cabinet in 1955.
 However he continued to sit as an MP for Woodford until he retired from politics in 1964.
 Churchill died on 24 January 1965 and was granted the honour of a state funeral.
 He was buried in his family plot in St Martin's Church, Bladon near to where he was born at Blenheim Palace.