A new law has come into force entitling workers who were paid less than the national minimum wage in a previous job to claim back-pay from former bosses.
The law means that employees who were paid less than the minimum wage in a previous job can now force their former employer to make up the difference.
Underpaid workers are already entitled to back-pay from current employers, but former employers have until now been able to escape liability because of a loophole in the 1998 legislation which introduced the minimum wage.
Trade unions said the new law would help underpaid employees claw back what they are owed.
Keeping up the pressure
"Our experience has been that many low paid workers only have the confidence to complain about underpayment after they have left the offending employer," said Brendan Barber, General Secretary of the Trades Union Congress.
"The government has already recovered £13m for workers cheated out of the minimum wage. This law will help them keep up the pressure and ensure that there is no hiding place for bad bosses."
Employment relations minister Gerry Sutcliffe said the government's determination to close the loophole in the National Minimum Wage Act demonstrated that it was "not complacent in enforcing rules, and would tighten them up where necessary."
The minimum wage, currently set at £4.20 an hour for adults aged 22 or over, is set to rise to £4.50 an hour in October.
Workers aged 18 to 21 will see their hourly rate rise from £3.60 to £3.80.
Anyone who thinks they are not being paid the minimum wage is being advised by the government to contact the enforcement helpline on 0845 6000 678 or use the government's Tiger.gov.uk website (see link on right).