Marks & Spencer staff have been trying out "inspirational dancing" as part of team building exercises aimed at reversing the ailing retailer's fortunes. New York business guru and motivator Mary Gober has been drafted in by M&S boss Stuart Rose to run a series of sessions for the 55,000 shop staff, including one in Birmingham.

The company said it would help staff provide "a better service for our customers" but shopworkers' union Usdaw described it as a £10 million waste of money. M&S would not reveal the bill, but said it was less than that.

On her website, retail motivationist Ms Gober is dubbed "the most dynamic force in customer service culture development today", whose "expertise and knowledge in the field is unrivalled". On Tuesday, around 5,000 M&S staff were at the National Exhibition Centre for the first of the day-long "dress down" sessions where they took part in activities such as "inspirational dancing in the aisles".

Many staff turned up in fancy dress and each was given a goodie bag with nine envelopes to be opened on Ms Gober's instruction.

They included questions about whether people were "fun to be with" or "cynical and moody". Another contained a dollar bill with the slogan: "Don't pass the buck."

A further 5,000 staff were at the NEC for a similar session yesterday and another session will take place today.

A spokeswoman for M&S said: "We are training all of our customer service assistants to enable them to provide a better service for customers. It is part of a three-pronged strategy to improve the look of stores, the range of products, and customer services."