Brightest light of our world gone out: David Cameron on Nelson Mandela

British Prime Minister David Cameron today paid his tribute to Nelson Mandela after his death and said "the brightest light of our world has gone out".

"One of the brightest lights of our world has gone out. Nelson Mandela was not just a hero of our time, but a hero of all time, the first president of a free South Africa, a man who suffered so much for freedom and justice," Cameron said.

The flag above Downing Street is flying at half-mast as a mark of respect, the BBC said.

Cameron said Britain shared with South Africa this moment of grief and recalled the strongest impression of meeting him was his "extraordinary compassion and generosity and forgiveness".

"Tonight, families across Britain will mourn with his family and everyone in South Africa. Your greatest son has moved millions and I believe that his inspiration for the future will be every bit as powerful as the extraordinary things he achieved in his remarkable life," he said.

Speaking outside Downing Street, the prime minister said, "Meeting him was one of the great honours of my life...My heart goes out to his family - and to all in South Africa and around the world whose lives were changed through his courage".

The Duke and Duchess of Cambridge, who were watching a film premiere about the life of Nelson Mandela in London when news of the former South African president's death emerged.

"It's extremely sad and tragic news. We were just reminded of what an extraordinary and inspiring man Mandela was. My thoughts and prayers are with him and his family right now," Prince William said after the film.