Post-war leader Clement Attlee and 1980s titan Margaret Thatcher were named Britain's most effective 20th-century prime ministers in a study of British premiers for BBC History Magazine.
The pair outscored World War II prime minister Winston Churchill and were rated far higher than current incumbent Tony Blair, who was judged to have been hamstrung by the war in Iraq.
The 20 prime ministers were ranked with a score of one to five by historian Francis Beckett on how well they implemented their visions for changing Britain.
The Conservative Party's Thatcher, who led Britain from 1979 to 1990, scored a maximum five points alongside Attlee.
Beckett said that was because Thatcher "took one sort of society, and turned it into another sort of society".
He chose her 1985 victory over striking miners as a crucial landmark.
"Few people under 40 remember a time when trade unions were a real force in the land, when the public sector controlled large swathes of the economy, when local councils controlled education and other local services, when benefits were considered rights of citizenship," he said.
"The defeat and destruction of the once-powerful National Union of Mineworkers was a key moment."
Thatcher, her successor John Major and Blair are the only living people on the list.
Attlee led the Labour Party government from 1945 to 1951, which nationalised industry and established the welfare state, creating an enduring consensus, which was dismantled by Thatcher's reforms.