1) Harold Wilson
2) Boris de Pfeffel Johnson
3) Gordon Brown
4) Margaret Thatcher
Explanation:
British politician & a Leader of the Conservative Party Boris de Pfeffel Johnson(55), who has promised to lead Britain out of the European Union(28-nation bloc) with or without a deal by the end of October 2019 won the contest to be the British prime minister(PM) succeeds Theresa May,who got stepped down over her failure to get parliament to ratify her Brexit deal.