THREE former Prime Ministers, Tony Blair, Gordon Brown and Sir John Major, will join David Cameron today at the official memorial ceremony for Nelson Mandela in South Africa.

It is thought to be the first time for many years that all of the UK's surviving premiers have travelled to an event abroad, reflecting the deep respect in which South Africa's first black president is held by British politicians.

The event at the FNB soccer city stadium in Soweto township, Johannesburg, will also witness the unusual sight of US President Barack Obama making a speech on the same platform as Cuban President Raul Castro.

As well as Mr Obama, Air Force One also had on board his predecessor at the White House, George W Bush, and their wives. Flying separately to Johannes-burg were former Presidents Bill Clinton and Jimmy Carter. The only surviving former president not to travel was Mr Bush's father, George H W Bush, who is 89.

Ben Rhodes, White House deputy national security adviser, said: "I think it's a unique experience, and I think they all are remembering their different interactions with Nelson Mandela and his family. He was a leader who intersected with so many different American political leaders of both parties over the years."

More than 70 leaders from around the world will congregate to commemorate the life of the late anti-apartheid leader, joining an estimated 80,000 ordinary mourners.

Jacob Zuma, the South African President, will give the main addresses, leading the tributes to the country's first democratically-elected leader.

Other speakers will include Ban Ki-moon, the UN Secretary General, Li Yuanchao, the Chinese Vice-President and Hifikepunye Pohamba, the Namibian President. Members of Mandela's family and close friends will also speak at the ceremony, which will include a religious sermon.

The UK delegation will also include Nick Clegg, the Deputy Prime Minister, and Ed Miliband, the Labour leader.

It is unusual for both the PM and his deputy to attend an event to represent the UK. No 10 knocked back any suggestion the Liberal Democrat leader had insisted his name be on the guest list, stressing how it had been drawn up by the South African Government.

Entrepreneur Sir Richard Branson and pop singer Peter Gabriel - who devised "The Elders" forum of statesmen and activists set up by Mandela - are also due to attend.

The FNB stadium was the venue of the late President's final public appearance at the closing ceremony of the 2010 football World Cup.

Thousands of police will be on duty there and will block access to the site if crowds become too large, officials said, as South Africans continued to pay tribute to the former leader.

A spokesman for the South African Police Service, said "thousands" of officers will direct traffic, protect mourners and help the bodyguards of visiting dignitaries. "We will be on hand to make sure people are able to grieve in a safe environment."

A joint taskforce of police, diplomats and intelligence service personnel have been making plans and talking to the foreign delegations who are to attend the ceremony. Yesterday, workers installed bulletproof glass to protect the stage from where officials will make their speeches.

After the memorial service, Mandela's body will lie in state at South Africa's seat of government, the Union Buildings in Pretoria, until he is laid to rest in a state funeral at his hometown of Qunu in the Eastern Cape.

The Prince of Wales, repres-enting the Queen, will be among a smaller number of dignitaries travelling to the remote rural location for the service on Sunday.

The Queen is expected to attend a service of thanksgiving for the life of Mr Mandela at Westminster Abbey in the new year. Flowers have continued to be laid at the late President's statue in Westmin-ster's Parliament Square. He came to the UK for its unveiling in 2007.

A civic event will take place later this week at Westminster Hall, where Mr Mandela addressed both houses in 1996.