A handwritten letter from anti-apartheid leader Nelson Mandela is among formerly top-secret records which have been made available online for the first time.

John Astor and Sir John Maud used their connections to ensure the books avoided scrutiny from the South African authorities and reached Mandela

In the letter – dated September 14, 1962 and addressed to the British Embassy in Pretoria – Mandela thanks Sir John Maud, the British Ambassador in South Africa, and John Astor, editor of The Observer newspaper, for their help in ensuring he received books to help him study while he was in prison.

Mandela received six books – A Short History of Africa by Roland Oliver and JD Fage; A History of Europe (Vol I and II) by Hal Fisher; Essays in Biography by JM Keynes; Anatomy of Britain by Anthony Sampson; and The Making of the President by Theodore H. White – while in prison in South Africa.

It is not known whether a further five books, including My Early Life by Winston Churchill, reached him.

Mandela, who was jailed for 27 years during the struggle to replace the apartheid regime of South Africa with a multiracial democracy, refers to the books as a “valuable present” in the letter and thanks “his friend in England” Astor.

Under Astor’s editorship, The Observer supported the African National Congress, which Mandela supported and later led, from the early years of apartheid.

Astor and Sir John used their connections to ensure the books avoided scrutiny from the South African authorities and reached Mandela, who went on after his release from prison in 1990 to become the country’s first black President and to win the Nobel Peace Prize.

The letter, made available online to mark World Book Day, is contained in previously top-secret government records on Mandela’s arrest and trial, which are on show at the National Archives in Kew, southwest London.

The records reveal that during his time in prison, Mandela was studying for a law degree as an external student of London University. He passed the London Intermediate exams in 1963, but the conditions imposed by the South African authorities prevented him from completing the degree.

Simon Demissie, records specialist at the National Archives, said: “Mandela’s handwritten letter is a great example of the honour and respect which he spent many years struggling for.

“We are delighted to have this preserved in the collection at the National Archives and to make it available online so that people across the globe can appreciate this unique piece of history from the man himself.”