Prince Harry, Desmond Tutu, David Cameron and others honor memory of Nelson Mandela in London

Britain's Prince Harry, left, walks with John Hall, Dean of Westminster Abbey to attend the Nelson Mandela memorial service at the Abbey in London Monday, March 3, 2014. Mandela the former president of South Africa died in December 2013. (AP Photo/Alastair Grant) (The Associated Press)

British actor Idris Elba who portrayed Nelson Mandela in a recent film arrives for the Nelson Mandela memorial service at Westminster Abbey in London Monday, March, 3, 2014. Mandela the former president of South Africa died in December 2013. (AP Photo/Alastair Grant) (The Associated Press)

Daughter of the late Nelson Mandela, Zenani Mandela-Dlamini arrives for the Nelson Mandela memorial service at Westminster Abbey in London Monday, March, 3, 2014. Mandela the former president of South Africa died in December 2013.(AP Photo/Alastair Grant) (The Associated Press)

Prince Harry, former Archbishop of Cape Town Desmond Tutu, and Prime Minister David Cameron have joined nearly 2,000 people in a memorial service for the late South African President Nelson Mandela.

Tutu said Monday at the Westminster Abbey celebration that the anti-apartheid campaign in Britain helped keep the movement going.

He said campaigners had helped change the moral climate and prevented Mandela from spending his life in prison and being regarded by many as a terrorist.

Tutu thanked Britons who had picketed South African government buildings in London and led boycotts against the apartheid regime.

Mandela died in December. He had often cited the British judicial system as a model.

The centuries-old Abbey resounded with the sounds of South African singing and drumming during the service.