Sports Direct, Britain's biggest sportswear retailer, responded to critics of its employment practices today with the launch of a review of conditions for its thousands of agency warehouse workers.

The review will be overseen by its billionaire founder and majority shareholder, Mike Ashley. 

The FTSE 100 company, under fire from media, investors and politicians, also hit back at what it called "unfounded criticisms", issuing a long list of rebuttals. 

A report by the Guardian newspaper last week said that protracted security checks of workers at its main warehouse in England, meant that some were effectively paid less than the legal minimum, an allegation denied by the company. 

On Monday, the firm was criticised by lawmakers in Britain's parliament and a government minister said it would face sanctions if it flouted wage laws. 

The review will include the operation of "the strike system", which the firm uses to assess workers' performance. 

"The board has agreed that Mike Ashley shall personally oversee a review of all agency worker terms and conditions to ensure the company does not just meet its legal obligations, but also provides a good environment for the entire workforce," Sports Direct said today. 

In November the Shirebrook facility in England used about 4,300 agency workers. 

Sports Direct has a global workforce of 28,000, of which about 20,000 are employed in the UK. 

Ashley, who owns 55% of Sports Direct's equity and currently serves as the firm's deputy chairman, will start the review next month. 

Starting with a single sports shop 33 years ago, Ashley has managed to develop a business with 400 stores across the UK and operations in 20 other countries. He is also the owner of soccer club Newcastle United and clothing retailer Heatons. 

Sports Direct's share price has fallen 18% over the last month, following the publication of disappointing first-half results on December 10. 

Sports Direct defended its use of agency workers at its warehouse, saying the two main agencies it uses also supply workers to hundreds of companies nationally on the same core terms and conditions. 

It also said neither agency workers nor employees were subjected to "naming and shaming" via publication of a league table identifying individuals by name. 

And it denied allegations that the warehouse tannoy was used to "harangue" staff, that it penalised staff for being ill and that it discriminated on the basis of nationality. 

The firm said it was not alone in using casual workers in its retail operations, with many other store groups using "zero hour" contracts in their shops. 

It also said a "significant" number of casual workers have moved from "zero hour" terms into permanent employment when the circumstances allowed, including Dave Forsey, its current chief executive.