More than one million British workers are employed on controversial zero-hours contracts, figures released yesterday revealed, suggesting that British business is deploying the employment terms far more widely than previously thought. The figure - derived from a poll of more than 1,000 employers conducted by the Chartered Institute of Personnel and Development (CIPD) - prompted renewed calls for the government to launch a full inquiry into the use of the contracts, after a week in which organisations from retail chains to Buckingham Palace have faced criticism for hiring staff but offering no guarantee of work and pay each week. Employees on zero-hours contracts often get no holiday or sick pay and have to ask permission before seeking additional work elsewhere. The CIPD found that 38 per cent of zero-hours contract workers described themselves as employed full-time, working 30 hours or more a week. One third of voluntary sector employers use the contracts, and one in four public sector organisations. The latest numbers also call into question the accuracy of official data. Last week, the Office for National Statistics increased its estimate of the number of zero-hours workers by 25 per cent, to around 250,000. Peter Cheese, the chief executive of the CIPD, said: "Our research suggests they are being used more commonly than the ONS figures would imply. There does need to be a closer look at what is meant by a zero-hours contract, the different forms that they take, and clearer guidance on what good and bad practice in their use looks like. And this needs to consider both the advantages and disadvantages in practice for businesses and employees." Last week, Sports Direct became the focus of controversy when it emerged that the retailer employs around 20,000 of its 23,000 staff on the contracts. The revelation was followed by details of a string of other companies using the deals, including cinema chain Cineworld and Buckingham Palace, which uses them for its 350 summer workers. Business secretary Vince Cable is conducting a review, which the opposition Labour Party says is "totally inadequate" and not comparable to a formal inquiry. Vidhya Alakeson, deputy chief executive of think tank the Resolution Foundation, said: "If it's true that there are in the region of one million people on zero-hours contracts, then that would be a substantial portion of the workforce. This could no longer be dismissed as an issue affecting only a tiny minority." Unions have accused employers of pressuring staff into signing the contracts as a way to cut staff benefits.