At the end of last year there was a clamp down on the Fashion Industry, the main target was companies that advertise for unpaid trainees (interns). Its likely this will lead to an even bigger campaign in 2014.
Current minimum wages rates are
21 Plus £6.31
18 to 20 £5.03
Under 18 £3.72
If you take on unpaid trainees without a contract you could be at risk of a £5,000 fine. The penalty can also apply if you are paying below the minimum wage.
If you find that you are paying below NMW you need to correct the rate of pay now and back date it to avoid the risk of a penalty.