The Co-op is to switch all its own-brand chocolate bars to the ethically-sound Fairtrade label.

The move, if successful, would double sales of Fairtrade chocolate in the UK jumping form £3m to £6m, the Co-op said.

Head of brands at the Co-op, Terry Hudghton, said the group would continue to increase its other Fairtrade lines. But that it has made chocolate its primary focus because of the “obscene contrast between the pleasure derived from eating it and the suffering that can go into supplying its key ingredient”.

Multinational chocolate manufacturers came under fire last year when a BBC investigation revealed the presence of child slave labour in West Africa.

Hudghton said: “If the major manufacturers were to carry just one Fairtrade product in their range the benefits for the poverty-stricken cocoa growers would be phenomenal.

“And if other supermarkets followed the Co-op’s Fairtrade lead, chocolate manufacturers would have to bow to commercial pressure.”