Question: Which British Prime Minister was the target of an alleged blackmail plot by the KGB and the Czechoslovakian secret service (StB)?

Context articles: Michael Karpin
Carmine Pecorelli
Prime Minister's Official Spokesperson
Jaroslav Svěchota
Heath Caper
Spencer Perceval
2007 royal blackmail plot
Ivan Lexa
Margaret Thatcher
Edward Heath

Michael I. Karpin (Hebrew מיכאל קרפין, born on 29 November 1945) is an Israeli broadcast journalist and author, best known for his investigative documentaries and books, revealing two of Israel's most concealed affairs: The creation of the country's nuclear capability and the nationalistic-messianic incitement campaign that preceded the assassination of Prime Minister Yitzhak Rabin.
 On May 1986, Karpin broke the story of Israel's secret service (Shabak) fabrication of evidence in the course of Bus Line 300's investigation, one of the most controversial political affairs in the history of the country.
 In 1987, he exposed the Izat Nafsu Affair: a Moslem IDF officer and a Circassian (a small ethnic minority in Israel), who was maliciously investigated by the secret service, convicted of spying and eventually exonerated by the Supreme Court.
 Karpin is married to Pnina (née Bahat), has 3 grownup children and lives in Tel Aviv.
Carmine Pecorelli (September 14, 1928 – March 20, 1979), known as Mino, was an Italian journalist, shot dead in Rome a year after former prime minister Aldo Moro's 1978 kidnapping and subsequent killing.
 He was described as a "maverick journalist with excellent secret service contacts."
 According to Pecorelli, Aldo Moro's kidnapping had been organized by a "lucid superpower" and was inspired by the "logic of Yalta".
 Pecorelli's name was on Licio Gelli's list of Propaganda Due masonic members, discovered in 1980 by the Italian police.
 In 2002, former prime minister Giulio Andreotti was sentenced, along with Mafia boss Gaetano Badalamenti, to 24 years' imprisonment for Pecorelli's murder.
 The sentence was thrown out by the Italian Supreme Court in 2003.
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.
Jaroslav Svěchota, plk., JUDr.
 (September 13, 1941 – November 8, 2004) was the former Deputy Chief of the Slovak Secret Service and lawyer.
 Together with Ivan Lexa, Svěchota was one of the key figures in the controversial reign of Prime Minister Vladimír Mečiar in Slovakia in the mid-1990s and was an important figure in numerous trials concerning the Secret Service both as witness and defendant.
The Heath Caper was an alleged plot by the KGB and the Czechoslovakian secret service (StB) to gain blackmail leverage over British Conservative politician Edward Heath.
Spencer Perceval, {'1': ", '2': ", '3': ", '4': "} (1 November 1762 – 11 May 1812) was a British statesman who was Prime Minister of the United Kingdom from 1809 until his assassination in 1812.
 Perceval is the only British prime minister to have been murdered.
 He was also the only Solicitor General or Attorney General to become Prime Minister.
The 2007 royal blackmail plot was a UK scandal in which two men attempted to blackmail a relation of the British Royal Family.
 The relative of the royal family was alleged to have been involved in activities involving drug taking, and performing sexual activity on a male aide.
Ivan Lexa, Ing.
 (* August 18, 1961, in Bratislava) is the former head of the Slovak Secret Service from 1995 to 1998.
 One of the closest allies of the former autocratic Prime Minister of Slovakia Vladimír Mečiar, under Lexa the Secret Service committed numerous high-profile politically motivated crimes.
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.
 She was the longest-serving British prime minister of the 20th century and the first woman to have been appointed.
 A Soviet journalist dubbed her the "Iron Lady", a nickname that became associated with her uncompromising politics and leadership style.
 As Prime Minister, she implemented policies that have come to be known as Thatcherism.
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.
 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.
 It was, says biographer John Campbell, "Heath's finest hour".
 Although he planned to be an innovator as Prime Minister, his government foundered on economic difficulties, including high inflation and major strikes.
 He became an embittered opponent of Margaret Thatcher, who supplanted him as party leader in 1975.