Sports Direct's shareholders are being urged to block the re-election of Mike Ashley to the board as the tycoon comes under increasing pressure over the retailer's working practices.

Shareholder lobby group Pensions Investment and Research Consultants (Pirc) wants investors to oppose the billionaire's re-appointment as executive deputy chairman, following demands from MPs that he be "held accountable" for the "appalling" practices at its shops and warehouses.

Pirc, which advises clients with assets of more than £200 billion, said it also has "significant concerns" about Mike Ashley's "influence on the board" and whether other directors can "objectively challenge and influence" the board's decision-making process.

It added that chairman Keith Hellawell should also be ousted after he "failed to show leadership in a critical period for the company."

It comes ahead of the retailer's annual general meeting on September 7 when investors will vote on whether an independent review should be launched into how the firm treats its staff.

Pirc wants shareholders to back the resolution put forward by Unite union for an independent review into the retailer's human capital strategy.

However, the FTSE 250 firm is expected to anger shareholders further after it was revealed that the retailer's accounts do not disclose that international deliveries are run by Mr Ashley's brother, John Ashley.

Sports Direct pays Barlin Delivery - run by the founder's older brother - a share of the revenues generated by orders that are dispatched overseas.

The firm announced last week that thousands of its warehouse workers will collectively be handed £1 million in back pay after the retailer came clean over not paying the national minimum wage.

In a deal struck with HMRC and Unite the union, the retailer will provide payments dating back to May 2012, with some staff pocketing up to £1,000.

Mr Ashley told MPs from the Business Select Committee in June that staff were not paid during security searches at the end of their shift, meaning they took home less than the minimum wage.

The under-fire retailer said the findings of a separate independent review carried out by law firm RPC would be published in the week beginning September 5 and it would conduct a review of its board of directors by next April.