Social networking can be a harmless forum in which staff act as eager brand ambassadors. Then again, it can also be a backfire spectacularly.

After Ryanair’s short-lived Twitter account last year in which staff are said to have described passengers as “mostly stupid” and “smelling of urine”, staff at shops owned by the Dixons Stores Group have been caught insulting customers on Facebook.

‘DSGi Employees’, an unofficial group, set up for staff and former employees of DSG, has 30,000 members. But DSG management were alerted to to news that it featured comments labelling customers "stupid" and heaping insults on them. One member of staff at a store asked if it would be acceptable to use a cattle prod on unsatisfied customers.

"We have clear guidelines for staff and will investigate any alleged abuse of customers,” said a spokesman for DSGi. "Delivering excellent customer service is at the forefront of everything we do, and so we are very disappointed that a small number of our colleagues have made these comments on a social-networking website. We will take the necessary action with any staff found to be acting inappropriately."