Accusation day after Wonga agrees to remove its branding from childrens' replica shirts - but not until 2016/17 season

In a speech Mr Miliband will say Sports Direct is a “bad place to work” and pledge that under a Labour Government the exploitation of zero-hours contracts will be banned.

In a major speech, Mr Miliband will liken the firm’s behaviour to “Victorian management practices”, an era normally associated with children working in factories and mines and up chimneys.

And he will say: “Sports Direct has thousands of its employers on zero-hours contracts, the vast majority of its workforce.

“Sports Direct has predictable turnover, it is a modern company with stores on many high streets and - judging by its success - where many people shop.

“But, for too many of its employees, Sports Direct is a bad place to work.

“These Victorian practices have no place in the 21st Century and, under a Labour government, the exploitation of zero-hours contracts will be banned.”

The attack will see the embattled Mr Miliband return to the theme of his early years as leader, when he targeted companies he once accused of ruthless “predatory” practices.

It follows the revelation, early this year, that Sports Direct is the biggest employer of part-time staff on zero-hours contracts that them getting a second job.

It emerged that more than eight out of ten of the retail empire’s 20,000 workers have no guaranteed working hours and must seek permission from management to work elsewhere.

Meanwhile, Mr Ashley himself has a personal fortune estimated to be £3.75bn, according to the Sunday Times Rich List.

A legal action by a former employee then forced Sports Direct to advertise the limitations of working under zero-hours contracts, after a settlement was agreed.

The retailer will have to make clear - in job advertisements, contracts and staff-rooms - that it does not guarantee work, sick pay or holiday pay.

Meanwhile, the Coalition Government has vowed to ban employers from requiring such workers to work exclusively for them, estimating some 125,000 workers will benefit.

But, in today’s speech in Birmingham, Mr Miliband will describe that move as a minor tweak – pledging instead to outlaw zero-hours contracts altogether, for those that staff that oppose them.

Aides pointed out that store managers at Sports Direct work full time and receive a generous bonus – something denied to zero-hours sales assistants

Under Labour’s plans, legislation will give employees the legal right to: 

•  A regular contract, if they are working regular hours.
•  Refuse demands that they make themselves available over and above their contracted hours.
•  Compensation when shifts are cancelled at short notice.

Mr Miliband will say: “Zero-hours contracts are becoming the norm in parts of our economy. Their numbers have increased to 1.4m since this Government came to power.

“It has left too many people not knowing how they will make ends meet from one week to the next and unable to plan for the future. And this government won’t do anything to stop it. but we will.

“This is not about exceptional use of zero-hours contracts for short term or seasonal work which some employers and workers may find convenient - this is the way Sports Direct employs the vast majority of its workforce.

“Under Labour, if you work regular hours you will have a legal right to a regular contract.”

The news comes a day after controversial pay day lender Wonga bowed to pressure from MPs and agreed to drop its logo from all children’s Newcastle United replica shirts.

Mr Miliband will say: “Zero-hours contracts are becoming the norm in parts of our economy. [They] have left many people not knowing how they will make ends meet from one week to the next and unable to plan for the future. And this government won’t do anything to stop it. but we will.”

Sports Direct has previously refused to comment on revelations that it is the biggest employer of part-time staff on zero-hours contracts, which prevent them from getting a second job.

Wonga, meanwhile, said its move would not happen until the start of the 2016/17 season, leading fans’ representatives to say it did not go far enough and them calling on the club to end its relationship entirely with the company.

Last month Wonga, which became infamous for sky high rates of interest and its ‘cuddly’ puppet television characters, said it was writing off £220m of debt to 330,000 customers after admitting it did not carry out adequate affordability checks on the loans.

It said this latest move was part of a change of strategy to prevent its marketing appealing to young or vulnerable people.

Newcastle Central MP Chi Onwurah, who had joined other North-East MPs in demanding the removal of the logo, said: “I’m pleased [Wonga] have agreed to remove their logo from kids’ strips. “At least my heart won’t sink when I see five year-olds wearing it on matchdays.”

However the MP criticised the length of time Wonga was taking, with the firm claiming kit production schedules meant the start of the 2016/17 season was the earliest point it could make the change.

Mark Jensen, editor of themag.co.uk, said: “It is welcome news and is not before time, but I suspect Wonga has been left with no option.

“They are not a suitable sponsor for kids to wear on shirts – a legal loan shark is not what Newcastle United should be getting in bed with.

“There are surely a lot more sponsors out there who would be more appropriate.”

The club’s spokeswoman did not respond when contacted by The Northern Echo, although its official Twitter account retweeted the announcement by Wonga.

The move coincided with the launch by Newcastle United Supporters Trust of a partnership with three local credit unions which will offer a specially branded account giving regular savers access to low cost loans.