Tesco has stopped the production of its charity Christmas cards after a six-year-old girl found a note allegedly from a prisoner in a Chinese warehouse forced to work.

Florence Widdicombe, 6, from South London found a message written inside one of the cards that said: “We are foreign prisoners in Shanghai Qinqpu prison China. Forced to work against our will. Please help us and notify human rights organization.”

The note also urged for whoever found the note to contact former journalist Peter Humphrey, who spent 23 months in the same prison according to the Sunday Times.

Humphrey said he contacted his former ex-prisoners. One prisoner said the inmates in the foreign prisoner unit had been picking and packing Tesco cards for at least two years.

A spokesman for Tesco said: “We abhor the use of prison labour and would never allow it in our supply chain. We were shocked by these allegations and immediately suspended the factory where these cards are produced and launched an investigation. We have also withdrawn these cards from sale while we investigate.

“We have a comprehensive auditing system in place and 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. If a supplier breaches these rules, we will immediately and permanently de-list them.”

Tesco is associated with three charities – the British Heart Foundation, Diabetes UK and Cancer research UK – and donates £300,000 a year to them from the sale of boxes of Christmas cards.

It is understood they will still receive the full donation this year, according to the Sunday Times.