Somerfield has left the Ethical Trading Initiative, an alliance set up to ensure that suppliers in developing countries meet basic working conditions.

A spokesman for the supermarket group said: “We have taken the decision not to renew our membership… but we will continue to invest in our monitoring and audit systems to ensure that we source from suppliers with approved standards of employee welfare.”

The Ethical Trading Initiative added: “Somerfield informed us that the decision was taken after the company entered private ownership, which prompted them to reconsider their short- and medium-term business priorities.”

Meanwhile, Sir Terry Leahy, chief executive of Tesco, is expected to reveal plans this week to make the retailer a “better neighbour”.

Sir Terry will unveil the plans, which are expected to include the environment, health and local communities, in a speech at the Work Foundation, on Wednesday.