The move follows the decision by Tesco shareholders last month to reject a call from TV chef Hugh Fearnley-Whittingstall to upgrade the store's minimum chicken rearing conditions to the RSPCA's "Freedom Food" marque.

In a Commons motion yesterday, signed by 26 MPs, Liberal Democrat Bob Russell urged all food retailers to adopt the RSPCA's standard and said consumers should boycott Tesco chicken until it did so. The motion called on the Government to make the RSPCA standard a legal requirement.

Mr Fearnley-Whittingstall tabled a resolution at the retailer's AGM in an attempt to force the change but the resolution, which needed the approval of at least 75 per cent of shareholders to be passed, won just under 10 per cent of the vote.

Tesco insisted it exceeded minimum legal standards for chicken rearing and all its farms were independently audited.

A spokeswoman said: "We subscribe to the Assured Chicken Production programme, whose standards provide for birds to have six hours of light each day, against the legal minimum of one hour."