Mike Ashley’s Frasers Group has again been accused of paying warehouse workers below minimum wage for the second time in five years.

Staff working at warehouses supplying the group, including Sports Direct, Flannels, Jack Wills and USC, are reportedly not being paid for half-hour breaks and are not able to leave the premises during breaks, according to an investigation by The Guardian.

The newspaper sent a reporter to one of Frasers’ warehouses over two weeks in late June and early July. With unpaid breaks, warehouse staff are effectively being paid £8.20 an hour – compared to the legal minimum of £8.72.

The Guardian previously reported that Ashley’s Sports Direct group had breached minimum wage laws in 2015. The investigation led to workers receiving £1m in back pay and led to Ashley answering to a parliamentary select committee.

MPs found that Sports Direct had treated “workers as commodities rather than as human beings” and saw the retailer conduct a review into its working practices which led to a string of changes in 2016.

In a statement, Frasers denied the latest accusations. It said: “The whole basis for [The Guardian’s] purported investigation is founded on a false premise – that a daily 30-minute rest break should be regarded as constituting working time and so paid. This is clearly not the case.”

Frasers also denied the accusation that staff were not permitted to leave warehouses during breaks and said it did not have to pay staff for breaks under the law. The retailer also said there was no legal requirement for it to provide separate facilities for staff during rest breaks.

The HMRC National Minimum Wage manual says “breaks are not typically counted as working time” but companies should make sure breaks are “genuinely taken”.

It also says: “Time where a worker… is not working but is required by their employer to be available at or near a place of work for the purposes of working is treated as working time for national minimum wage purposes, even if the worker is simply waiting to be given work, is ‘on-call’ or ‘stand-by’.”