As the Queen of Shops turned her attention to shoddy customer service in her new C4 programme Mary Portas: Secret Shopper, the Institute of Customer Service claimed some multiples have already pushed the issue to the top of their agendas.

The Institute's UK Customer Satisfaction Index identified Waitrose, Marks & Spencer and Iceland as the supermarkets with the most satisfied shoppers.

Lidl and The Co-operative Group were fingered as the poorest performers, after shoppers marked them down on staff professionalism, helpfulness and knowledge.

However, on the whole shopper satisfaction had increased in the past year, with the index recording a two-point improvement in service, said ICS director Duncan Baker, and the emphasis on staff training to ensure better service looked likely to continue rising.

The multiples had increased their focus on service at board level, he said. "Customer service is very much moving into the boardroom. People are realising they can only take price so far as a way of differentiating themselves. People are starting to see service as a strategic issue," he said.

In recent months Waitrose and Morrisons, which came fifth in the survey after Asda, have joined ICS training programmes in a bid to improve customer service.