The taxman is seeing employers trying to make up "crazy" excuses for not giving their staff the minimum wage, including one who claimed their employees were not entitled to be paid properly because they did not speak English.
HM Revenue and Customs (HMRC) said that in another case, its officers challenged an employer who claimed that a worker was his wife - before he asked her: "What's your name, love?"
It said some employers are treating the national minimum wage as if it is a "choice" - but those who fail to play by the rules face being fined and having to pay back pay to their employees. About £4 million of back pay was handed out as a result of HMRC's investigations last year.
The National Minimum Wage (NMW) Act came into force 15 years ago this week, on April 1, 1999. The minimum wage is £6.31 an hour for workers aged 21 and over, increasing to £6.50 in October 2014.
To coincide with NMW's 15th anniversary, HMRC has published a list of the worst excuses it has seen over the past 12 months for employers failing to pay the minimum wage.
They also include one employee fleeing the building when officers from HMRC arrived to check for wage infringements, only to return a while later and pretend to be a customer.
HMRC's nationwide network of enforcement teams investigate complaints, as well as educate employers and employees about what happens if they fail to pay their employees what they are owed.
Anyone who believes they are not being paid the minimum wage can call the pay and work rights helpline, in confidence, for advice, in more than 100 languages, on 0800 917 2368.
Calls to the helpline from interns who are working for nothing, or for "expenses only", are being fast-tracked to HMRC enforcement officers for investigation.
Jennie Granger, HMRC's director general of enforcement and compliance, said: "Most employers are honest and pay their staff the correct rate.
"But this research shows that some still view the national minimum wage as a choice, and will even try these crazy excuses to avoid paying workers what they are due.
"Last year, HMRC's investigations resulted in over 26,000 people getting a share of £4 million in back pay.
"HMRC investigate all complaints of employers failing to pay the minimum wage. We will take action to recover back pay for employees and fine employers who are not playing by the rules.
"HMRC officers work hard across the UK to ensure that everyone is paid at least the national minimum wage, and anyone who isn't should call us."
More information about the different minimum wage rates, which depend upon age and apprentice status, can be found at www.gov.uk/national-minimum-wage-rates.
Here are the worst excuses HMRC has seen given in the past 12 months for not paying the minimum wage:
1. An employer said a woman on the premises was not entitled to the minimum wage as she was his wife. When asked what his wife's name was, the employer said: "Err, her name? What's your name, love?"
2. One employer told HMRC: "My employees don't speak English, so they're not entitled to it."
3. An employee ran out of the premises when HMRC officers arrived to check for minimum wage infringements. The same employee then returned - minus the work pinafore - with the employer claiming they were a customer.
4. Another employer told HMRC: "When the NMW goes up I do increase the amount I pay a little, even if the total pay is still below the NMW. I don't think it's right to ignore rises in NMW."
5. Upon inspection, an employer told HMRC: "I know I am paying them too little, but they are happy to work for this amount because they are getting experience."
6. An employer said his employee was just working for a few days, with a view to buying the business. When HMRC checked food safety records, the employee's name was found on historic food temperature records.
7. An employer claimed they realised they were not paying employees the minimum wage and had just this week increased their wages - to an hourly rate which was still below the minimum wage.
8. An employer told HMRC: "It wasn't a conscious decision to say 'I'm not going to pay this', but I've never really considered doing it because I've not had people come to me and say: 'I'm not getting paid enough' or: 'Is this the minimum wage?'"
9. One employer claimed an employee was just a friend, and only in the restaurant as they were in the area. HMRC officers returned another day to find the employee in the kitchen preparing food.
10. A number of employers claimed that accommodation they provided workers made up for their shortfall in wages.
A statement from the Department for Business, Innovation & Skills (BIS) said: "Paying less than the minimum wage is illegal.
"The Government has brought in tough new enforcement measures against rogue employers. These include the new naming scheme and the introduction of higher financial penalties."