China Monday denied allegations that prisoners were being used for forced labour, after a British newspaper reported that a London schoolgirl found a message in a Christmas card claiming to be from inmates at Shanghai's Qingpu Prison.

Supermarket giant Tesco said at the weekend it had stopped production at a factory in China after one of its charity cards was found to contain a cry for help from a prisoner who made it, according to the Sunday Times newspaper.

But Beijing rebuffed the claims, which it said were "made up".

Geng also attacked former journalist Peter Humphrey who wrote the article -- who was himself detained in Qinqpu prison until his release in 2015 -- and said he had invented a "farce" to "hype himself up".

The note written in the card asked the person who found it to contact Humphrey, which the schoolgirl's father did. Humphrey then took the story to the Sunday Times.

"We are foreign prisoners in Shanghai Qingpu Prison China," said the message, in a charity card featuring a kitten in a Santa hat

"Forced to work against our will. Please help us and notify human rights organisation."