Some of South Africa’s most influential intellectuals and activists have urged David Cameron to reconsider his plans to repeal the Human Rights Act, warning that the move is reminiscent of the mindset that created apartheid.

In a letter to the Observer, 25 of the country’s most eminent playwrights, lawyers, politicians and artists say that more than two decades after the British people spoke out against apartheid in South Africa, it was their turn to reciprocate with support for a country that is in danger of betraying that honourable history.

Their intervention is timed to coincide with Mandela Day, the second since the anti-apartheid hero’s death. The signatories describe their “horror” at Cameron’s desire to replace the act with a British bill of rights. Britain’s role in challenging apartheid, they said, meant they had a duty to intervene on behalf of the British people.

Their letter states: “Rights do not belong to any one nationality – they must be universal. Dividing people, setting their rights and freedoms apart on the basis of their passport or race, stripping them of their human rights, led to the worst abuses of the 20th century. It led to apartheid. And it can only lead to further injustice and dispossession in the future.”

Among the signatories are Archbishop Njongonkulu Ndungane, a retired South African Anglican bishop and former prisoner on Robben Island, the prison colony where the apartheid regime held Mandela for 18 years, and key figures of the anti-apartheid movement such as Denis Goldberg, who was tried alongside Mandela and sentenced in 1964 to four terms of life imprisonment. Mandela, who died in December 2013, spent 27 years in prison, before becoming the country’s first black president in 1994.

The South African poet and writer Mandla Langa said: “I join the majority of humankind who hold that the international campaigns for the dismantling of apartheid in South Africa were strengthened by the authoritative voice of the people of Britain.

“Also believing that an injustice anywhere is an injustice everywhere, I am personally appalled that the British government plans to replace the UK Human Rights Act with measures that will certainly cause distress to many, many people.”

Goldberg said: “During the struggle against apartheid for human rights, Britain hosted one of the ANC’s main international offices.

“The people of Britain, through the anti-apartheid movement, gave us magnificent support because of their belief that human rights must be defended. It would be a sad day indeed to see Britain weakening its human rights legislation fought for over many generations and enacted by various governments.”

The Human Rights Act, which enshrines the European convention on human rights in British law, holds the governments of Europe to account, offering individuals protection against governmental excesses such as false imprisonment and torture.

Shami Chakrabarti, director of human rights group Liberty, which is campaigning to preserve the act, said: “Apartheid South Africa demonstrated just what can happen when the powerful pick and choose whose rights matter. Plans to repeal our Human Rights Act have already been condemned by victims of state abuse, all the devolved administrations, all the major opposition parties, Conservative MPs, the country’s greatest legal minds – and now by those who have lived through one of the darkest periods in modern history. What will it take for the government to listen?”

Archbishop Ndungane added: “Human rights are rights which a human being possesses by virtue of being a person, nothing else being taken into account. They are universal, inalienable and cannot be rationed according to nationality, skin colour, religion or wealth.

“In my country, human rights are enshrined into our constitution in order to ensure peace, freedom and a stable future for our citizens – and history shows that terrible things can happen when their universality is not enshrined explicitly into law.

“The UK’s commitment to the international human rights framework has long made it a beacon for those striving for freedom elsewhere. I urge the government not to extinguish that beacon with these misguided plans.”

Other signatories include South Africa’s best-known Aids activist, Zackie Achmat, the writer Breyten Breytenbach, who was imprisoned during the apartheid regime, and Pregs Govender, a feminist human rights activist and former ANC MP.