Lady Thatcher, who died in April aged 87, has come under fire for her resistance to tougher penalties on the South Africa regime during the 1980s, and faced accusations it was a selfish move to protect Britain’s business interests.
But Mr de Klerk, who along with Nelson Mandela oversaw the transition to ANC rule, said Thatcher and then US president Ronald Reagan had “helped to buy essential time for South Africa”.
“It is a pity that the Conservative Party has subsequently apologised for Thatcher’s opposition to sanctions,” he added.
Writing in the Times, Mr de Klerk argues that the handing over of power to the African National Congress (ANC) in the 1980s would have resulted in fighting and “the imposition of a communist regime” by the party’s left wing.
“Margaret Thatcher understood this,” he wrote. “Although she was a consistent critic of apartheid, she had no illusions about the challenges that we faced.
“She doggedly resisted demands for more sanctions and always gave me and our negotiating partners strong support for the achievement of a genuine non-racial constitutional democracy,” he added.
“In all likelihood an ANC victory before the mid-1980s could have been achieved only after a devastating racial war and would not have resulted in a genuine constitutional democracy but in the imposition of a communist regime.”