Cape Town — South African anti-apartheid icon Archbishop Desmond Tutu has warned that people who become "arrogant" and "drunk with power" will one day be nobodies in the country like the former apartheid leaders.

The Nobel Peace Prize laureate and former Anglican archbishop of Cape Town is among an array of church leaders criticising or turning their backs on the ruling African National Congress party before scheduled national and provincial election in South Africa on 22 April.

"Those who become arrogant, who become drunk with power, who seemingly are unassailable: watch out," Tutu said at a memorial service for veteran anti-apartheid politician Helen Suzman in Johannesburg on 1 March. "The Nats [the apartheid National Party] were returned election after election with an increasing majority. Where are they now?"

In Paarl, near Cape Town, another former anti-apartheid cleric, Allan Boesak, who was once president of the World Alliance of Reformed Churches, accused the ANC of standing by while he went to jail for "helping the struggle".

Boesak rose to prominence in the 1980s as a leader of the anti-apartheid United Democratic Front. He was for a time also the chairperson of the ANC in the Western Cape. He served a jail term in 2000 after conviction of fraud and theft of donor funds. He was readmitted to church ministry in 2005 after being pardoned by then president Thabo Mbeki.

"I went to prison because of money I used for the struggle," Boesak told about 1000 supporters. "The ANC knows but they do not have the courage to say it. I say to you that there is a God in heaven who will see to it that the truth comes out."

Boesak went on, "Fifteen years of disappointment is too long, 15 years is too long to walk on broken promises We look around and we see that our basic rights are still abused and our dignity is still denied, poverty has become the scourge of our people."

In Johannesburg, Tutu said that Helen Suzman, as a lone liberal fighter against apartheid for many years in the South African parliament may be gone, but her legacy of public service will always be exemplary for South African politics.

"Our freedom has been won from the endeavours of many stalwarts of many races. The nation owes its existence to a remarkably diverse group of races. No group can claim legitimacy through ethnicity. South Africa belongs to all who dwell here. All of us are sons and daughters of the land," said Tutu at the memorial service for Suzman. She died on 1 January, aged 91, at her home.

Tutu urged South Africa to learn through Suzman not to tolerate corruption.

A lawmaker in South Africa's parliament from 1953 to 1989, Suzman denounced racial segregation, ill-treatment of political prisoners and the erosion of the rule of law. For 13 years, from 1961 to 1974, she was the Progressive Party's sole representative and a lone liberal voice in the whites-only parliament.

Archbishop Tutu said Suzman's life should show South Africans that people could have different viewpoints and still show courtesy to each other.

"Public discourse should not sink to the level of the gutter," said Tutu. "Debate can be vigorous and animated, but in the end it has to be the cogency of the argument, and not the loudness and barbarity of language, that will win the day."