In the last year 200,000 workers were paid less than the minimum wage. This is the highest figure since the law was changed in 1999 to introduce minimum pay levels.
According to HMRC, the sectors most likely to pay staff too little are social care, commercial warehousing and the gig economy.
Alan Lewis, employment partner with Irwin Mitchell says: "The gig economy is a growing sector of minimum wage abuse as the number of businesses who are deemed to be engaging staff with worker status, rather than self-employed status, grows. HMRC are particularly keen on exposing such incorrect classifications of status and businesses would be well advised to be aware of this and check carefully the status of those they engage to perform work."
It does not matter how small an employer is, they still have to pay the minimum amount.
Government guidance is available for calculating the minimum wage for different types of work.
Tom Neil, of employment advice and conciliation service Acas, said firms which did not pay the national minimum wage were "breaking the law" and faced a maximum fine of £20,000 per worker. "Failure to pay the national living wage could also result in a company director being banned for up to 15 years," he added.