Anthony Sampson, the author and journalist, died peacefully aged 78 at his home on Saturday night.

He was a regular contributor to the Guardian and the Observer, and also served as a member of the Scott Trust, the Guardian's owner.

Mr Sampson was a close friend of Nelson Mandela, and in South Africa was the editor of the anti-apartheid magazine, the African Drum (now known as the Drum). He had recently revised his 1963 classic, The Anatomy of Britain, in an updated version, Who Runs This Place?, which was met with critical acclaim.

His 1975 book on the oil industry, The Seven Sisters, was awarded the Prix International de la Presse in Nice.

Mr Sampson's lifelong commitment to human rights and social justice began in the 1950s. After graduating from Oxford University, he was invited to South Africa to edit Drum.

He struck up strong links with the young ANC leaders Steve Biko and Nelson Mandela, and the latter later chose him to write his biography.

Paying tribute to his friend, Mr Mandela said at the time: "He cared about Africa in a way that is rare among those in the developed world, and he never stopped caring ... I knew that in his hands our cause would be reported justly."

Earlier this year, Mr Sampson was writing on the fall-out from the Iraq war, the use of torture, the monarchy, and the South African elections.

In 1993, he accepted an invitation to join the Scott Trust, leaving in 1996 after witnessing a period of significant change during which the trust bought the Observer.

In an article for the British Journalism Review in 1996, he attacked the disappearance of foreign news, parliamentary reporting and investigative journalism from newspapers.

Three years ago, Mr Sampson recounted how he joined Drum on receiving a telegram in 1951 from a former fellow student at Oxford offering him the editorship. Then aged 25, he jumped at the chance. In his words: "I knew nothing about business, journalism or Africa, so I went."

He leaves his wife, daughter, son and two grandchildren.