Sports DirectSports Direct will back-pay £1 million to some of its staff, after it was revealed the firm effectively paid below minimum wage at its warehouse in Derbyshire.

It is understood that some workers could receive a payment of up to £1,000, with the back-pay going back as far as May 2012.

It comes after an investigation by The Guardian, published late last year, revealed Sports Direct's security procedures took so long that staff were paid less that the minimum rate. The investigation also shined a light on strict working conditions, including a 'naming and shaming' policy for tardiness and performance deemed below par, docked wages for arriving even a minute late. The report claimed one female worker even gave birth in the toilets for fear of taking time off work.

Last month, the Business, Innovation and Skills committee said working conditions at the warehouse was similar to Victorian workhouses.

The news of back-payments for staff was described as a "significant victory" by Unite assistant general secretary Steve Turner. But he stressed that it does not mean working conditions will be improved.