They face losing £750 million in online sales unless they realise the power of recommendations made through social networking sites like Facebook.

A report by Royal Mail and The Future Foundation think tank found 66% of social networkers were more likely to buy something they had seen recommended, compared to 52% of those who were not involved in social networking.

A Royal Mail spokesman said:

"Retailers cannot afford to ignore this new generation of shoppers and those who tailor their sites to drive 'word of mouse' and understand how to interact with existing social networkers will benefit."