Zero hours contracts are more widespread than first realised, as research suggests that more than a million UK workers are signed up to the contracts, four times official estimates.

Research by the Chartered Institute of Personnel and Development showed that of the 1,000 employers surveyed, 3 to 4% of the whole workforce were on zero hours contracts.

Some 14% of these workers could not earn a basic standard of living, according to BBC News.

The Office for National Statistics suggested 250,000 workers were on zero hours contracts.

The findings come as Sports Direct has been criticised for signing 90% of its workforce up to the zero-hours contracts, which provide no guarantee of work or wages.

Boots has also come under fire for using the contracts. The health and beauty retailer states in its contract that employees may be asked to work abroad with little notice, according to the Mirror.

The contract states: “There is no requirement to be based permanently outside the UK - although you may be required to work abroad for short periods of time depending on the needs of your business.”

It adds: “The company cannot guarantee to provide a minimum number of hours per week. The company reserves the right to make changes to the hours and days you are required to work.”

Boots said its use of the contracts is “very limited” and that they give employees holiday and sick pay. It added: “If a zero-hour contract is used an early conversation takes place with candidates to understand availability. Both parties are then clear on the level of hours a candidate can commit to.”

In June, business secretary Vince Cable called for a review into the issue over the summer.

He said: “For some these can be the right sort of employment contract, giving workers a choice of working patterns.

“However for a contract that is now more widely used, we know relatively little about its effect…There has been anecdotal evidence of abuse by certain employers - including in the public sector.”

But shadow business secretary Chuka Umunna said zero-hours contracts should be the exception to the rule and called for a formal consultation.

He said: “While some employees welcome the flexibility of such contracts, for many zero-hours contracts leave them insecure, unsure of when work will come, and undermining family life.

“The ‘review’ the business secretary has established into zero-hours contracts is clearly inadequate given the seriousness of this issue and the mounting evidence of the abuse of zero-hours contracts.”