A Chinese printing firm that manufactures Christmas cards for British retailer Tesco has denied that it uses forced prison labour in its factories, days after a girl received a card containing a message from an inmate at Shanghai's Qingpu Prison complaining about conditions and asking for help.

Tesco said on Sunday that it had stopped production at a factory in China after the Sunday Times newspaper reported that a girl in south London had received the message.

"We are foreign prisoners in Shanghai Qingpu Prison China," it said, in a Tesco charity card featuring a kitten in a Santa hat.

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

But the factory manager told Chinese state media on Tuesday that the claims were "completely fabricated."

Speaking last week, a spokeswoman for Tesco, which is Britain's biggest retailer, said it was "shocked" and had "immediately halted production at the factory where these cards are produced".

"We would never allow prison labour in our supply chain," she said, adding that an investigation had now been launched.

She said the company had a "comprehensive auditing system in place".

'Prison labour'

"This supplier was independently audited as recently as last month and no evidence was found to suggest they had broken our rule banning the use of prison labour," she said.

"If evidence is found we will permanently de-list the supplier."

According to the Sunday Times, the note in the card — sold to raise money for charity — asked whoever received it to contact "Mr Peter Humphrey".

The girl's father searched for Humphrey online and discovered that he was a former journalist who had spent two years in Qingpu.

He got in touch with Humphrey, who contacted some other ex-prisoners, who confirmed that foreign inmates had been packing cards for Tesco.

Humphrey and his wife Yu Yingzeng, a naturalised US citizen, ran an investigative firm hired by pharmaceutical giant GlaxoSmithKline (GSK).

Arrested in 2013 on suspicion of illegally obtaining private data, he confessed on Chinese state TV but later claimed he was coerced. He and his wife were convicted in August 2014 and deported the following June.