Barack Obama's speech at yesterday's memorial service for Nelson Mandela was hailed as another one of his great oratory performances.

But it has been claimed today that the man who stood next to him on stage to translate his moving tribute into sign language was a FAKE, who had never been trained to sign and whose signals made absolutely no sense to deaf people.

The man also appeared alongside service organiser Cyril Ramaphosa and other world leaders as they spoke to a crowd of 80,000 at Johannesburg's FNB Stadium - with pictures of his gibberish gestures beamed around the world to millions more. Questions were first raised about the man's authenticity on Twitter, with the national director of the Deaf Federation of South Africa Bruno Peter Druchen tweeting: "Please get RID of this CLOWN interpreter, please!"

He later added: "This person is not using sign language at all, I am (a) deaf person myself...I use sign language every day."

South African Sign Language interpreter and trainer Francois Deysel said the man's signs "make no sense", and that he was just "moving his arms to try to look busy".

He added: "It is embarrassing and making a mockery of our profession."

South Africa's Deaf Federation later told the BBC World Service the man "is not recognised and has never been trained to sign", while the World Association of Sign Language Interpreters (WASLI) said he was not using any accepted form of sign language in the world.

Sheena Walters, from WASLI, told SBS news: “It seems quite obvious that the interpreter isn’t using South African sign language.

“Most sign languages across the world share a similar structure and pattern and this person seems to be making a lot of repetitive signs and isn’t displaying the usual facial expression or structure of sign language that you would normally see.”

Charlie Swinborne of The Limping Chicken - a British blog for deaf people - said the man appeared to be using a "strange repetitive rythmn", while occasionally swinging his shoulders.

They added: "On a day when the world saluted a man who fought oppression, a guy stood on stage and effectively oppressed another minority – deaf people, by making a mockery of our language."

"Above all I feel sorry for deaf South Africans, who should have had amazing access to the service, with a top-class interpreter there on screen, but got this instead."