Nelson Mandela urged thousands to join a global campaign against poverty yesterday, saying: "Like slavery and apartheid, poverty is not natural."

The former South African president made his call in London's Trafalgar Square, ahead of addressing finance ministers from the G7 industrialised nations later this week.

He told the crowds at the Make Poverty History Rally: "Like slavery and apartheid, poverty is not natural.

"It is man-made and it can be overcome and eradicated by the actions of human beings.

"And overcoming poverty is not a gesture of charity. It is an act of justice. It is the protection of a fundamental human right, the right to dignity and a decent life. While poverty persists there is no true freedom."

Mr Mandela, who visited Gordon Brown on Wednesday, after the Chancellor promised almost £530m for vaccines for children in poor countries, described poverty and inequality as the "terrible scourges of our times".

And he urged world leaders to act, saying: "Do not look the other way, do not hesitate. Recognise that the world is hungry for action, not words. Act with courage and vision."

On a personal note, Mr Mandela, who was released from prison in February 1990, said: "I can never thank the people of Britain enough for their support through those days of the struggle against apartheid.

"Many stood in solidarity with us, just a few yards from this spot.

"Through your will and passion, you assisted in consigning that evil system forever to history.

"But in this century, millions of people in the world's poorest countries remain imprisoned, enslaved and in chains. They are trapped in the prison of poverty. It is time to set them free."

Mr Mandela later travelled to Downing Street for talks with Tony Blair, Chancellor Gordon Brown and International Development Secretary Hilary Benn.