Question: What British Prime Minister did Wilberforce serve under who became party leader in 1975?

<P0-S0> Margaret Hilda Thatcher, Baroness Thatcher, {'1': ", '2': ", '3': ", '4': "} (née Roberts ; 13 October 1925 – 8 April 2013) was a British stateswoman who was Prime Minister of the United Kingdom from 1979 to 1990 and Leader of the Conservative Party from 1975 to 1990. <P0-S1>  She was the longest-serving British prime minister of the 20th century and the first woman to have been appointed. <P0-S2>  A Soviet journalist dubbed her the "Iron Lady", a nickname that became associated with her uncompromising politics and leadership style. <P0-S3>  As Prime Minister, she implemented policies that have come to be known as Thatcherism. <SEP> <P1-S0> Han Myeong-sook (born March 24, 1944; Korean: 한명숙 ] ) was the Prime Minister of South Korea from April 2006 to March 2007. <P1-S1>  She is South Korea's first female prime minister (second female prime minister overall if the acting premiership of Chang Sang is included). <P1-S2>  She was from the United New Democratic Party (UNDP) as a member of the Korean National Assembly (representative) for Ilsan-gab, and is a graduate of Ewha Womans University in Seoul with a degree in French literature. <P1-S3>  She resigned as Prime Minister on March 7, 2007 and declared her presidential candidacy. <P1-S4>  But she did not succeed in the nominations. <P1-S5>  In 2008 she ran for parliament, but was not elected. <P1-S6>  However, in January 2012 she was elected leader of the main oppositional Democratic United Party (DUP) before the April legislative elections and became a member of parliament. <P1-S7>  But the liberals did not manage to defeat the ruling Saenuri Party and Han stepped down as party leader in April 2012. <P1-S8>  In August 2015, Han was convicted of receiving illegal donations at the amount of 900 million KRW, and sentence to two years in prison. <P1-S9>  She is ineligible to run for public office for ten years after her prison term. <P1-S10>  She became the first former prime minister of the Republic of Korea to serve a prison time. <SEP> <P2-S0> Sir Edward Richard George Heath, (9 July 1916 – 17 July 2005), better known as Ted Heath, was a British politician who served as Prime Minister of the United Kingdom from 1970 to 1974 and Leader of the Conservative Party from 1965 to 1975. <P2-S1>  He was a strong supporter of the European Communities (EC), and after winning the decisive vote in the House of Commons by 336 to 244, he led the negotiations that culminated in Britain's entry into the EC on 1 January 1973. <P2-S2>  It was, says biographer John Campbell, "Heath's finest hour". <P2-S3>  Although he planned to be an innovator as Prime Minister, his government foundered on economic difficulties, including high inflation and major strikes. <P2-S4>  He became an embittered opponent of Margaret Thatcher, who supplanted him as party leader in 1975. <SEP> <P3-S0> Wilberforce was a cat who lived at 10 Downing Street between 1973 and 1986 and served under four British Prime Ministers: Edward Heath, Harold Wilson, Jim Callaghan and Margaret Thatcher. <P3-S1>  His chief function was to catch mice, in which role he was the successor to Peta. <P3-S2>  In life he had been referred to as "the best mouser in Britain", as befitted his role.