Helen Suzman: Bright Star in a Dark Chamber. By Robin Renwick. Biteback Publishing; 288 pages; £16.99. Buy from Amazon.co.uk

FOR much of the 27 years that Nelson Mandela was in prison, another South African led an almost equally solitary life, in purely political terms, by virtue of her role as the sole liberal member of parliament. Helen Suzman, a beacon of decency, courage and common sense, served as an MP from 1953 to 1989. For 13 of those years, from 1959, she was the only member for what was then the Progressive Party.

A lonely voice of reason, she tormented a succession of justice ministers with her barbed wit and penetrating questioning. A string of former political prisoners, including Mandela himself, testified to her courage and, perhaps even more important, to the effect she had in publicising and often alleviating the harshness of their conditions behind bars. Once the African National Congress (ANC) took over after the first democratic election in 1994, she never shrank from inveighing against its tendency to put party and state above the individual, whether black or white. She was the truest of liberals.

Robin (now Lord) Renwick, who until 2009 was chairman of the trustees of The Economist, served as British ambassador to South Africa from 1987 until 1991. He helped in critical ways to unravel the system from within. According to this crisply lucid account, Mrs Suzman was his closest ally. He is persuasive in presenting her as the doughtiest of fighters for human rights anywhere in the world—and one of the finest parliamentarians of her era.

At first becoming an MP for the tepidly reformist United Party, she broke away with a band of more liberal colleagues to form the Progressive Party in 1959. Two years later she was the only one of ten “Prog” MPs not to lose her seat.

Mrs Suzman used diligent research and her parliamentary prerogative to expose apartheid’s many abuses. She came to be admired by prisoners and their families from all opposition parties, but was also increasingly attacked for being “part of the system”, especially by the South African Communist Party (SACP), who played a leading role in the ANC in exile. A particularly nasty article appeared in 1971 in Sechaba, the ANC’s journal, under the name of its leader in exile, Oliver Tambo, though Lord Renwick implies that someone else actually wrote it. “Vorster [the then prime minister], Suzman and lesser agents of colonialism”, the article ran, “have turned Africa into a veritable hunting ground for stooges and indigenous agents of racism.” Mrs Suzman was accused of being “determined to prevent change”.

One charge against her and her fellow Progressives was that they had at first endorsed a qualified franchise, under which only educated blacks would have the vote. Later she was more roundly vilified by many in the ANC, in the SACP and by anti-apartheid campaigners abroad, for opposing blanket sanctions against South Africa. She reluctantly endorsed sports sanctions, but resolutely opposed academic and economic ones: they made whites more blinkered and defiant and blacks even poorer. Change, she said, would come only if the country’s rulers were forced to engage with the world outside.

While agreeing to disagree with her on economic sanctions, Mandela and other ANC luminaries recognised that Mrs Suzman’s struggle within the system had, in fact, been invaluable. After Mandela’s release from prison in 1990, she was prominent among those, according to the author, who persuaded him to drop the ANC’s revolutionary programme in favour of an evolutionary one, retaining a market economy and a parliamentary democracy. And she could even criticise Mandela, once ticking him off when he praised Muammar Qaddafi of Libya as a supporter of human rights with a brisk “How could you be so silly, Nelson!”

Mandela’s verdict, in any event, outweighs that of his party. “The consistency with which you defended the basic values of freedom and the rule of law over the last three decades has earned you the admiration of many South Africans,” he wrote from jail before his release. “None can do more than her duty on earth”, he wrote in a book inscription to her, shortly afterwards. It is he and she, not today’s ANC, who deserve the last word.