A law allowing workers to claim back-salary from former bosses who failed to pay them the National Minimum Wage came into force yesterday.

The legislation will enable the Inland Revenue to force firms to pay arrears to former, as well as existing, staff employed since last August who were not receiving the minimum wage.

It closes a loophole in the National Minimum Wage Act 1998 exposed by an employment tribunal in August last year.

The tribunal ruled the Act meant enforcement officers were unable to issue notices claiming arrears on behalf of former workers.

The Government said it has rectified the situation by bringing forward the National Minimum Wage (Enforcement Notices) Bill 2003.

A spokeswoman for the Department of Trade and Industry (DTI) said ministers had previously assumed the 1998 Act gave people the right to claim arrears for past, as well as current, jobs.

The Government had introduced the new bill to "clarify" the situation, she said.

The Inland Revenue is reviewing all cases that have arisen since the tribunal last August, the DTI said.

Employment relations minister Gerry Sutcliffe said the move showed the Government was "not complacent in enforcing rules".

"The Government is determined to make sure all workers get what they are owed," Mr Sutcliffe said.

On October 1, the minimum wage for adults aged 22 or over will rise from £4.20 to £4.50.

The development rate, for workers aged 18-21 inclusive, will increase from £3.60 to £3.80. Ministers say between 1.3 million and 1.6 million low-paid workers will benefit from the rises.

Brendan Barber, TUC general secretary, said: "The minimum wage is a useful protection for low-paid workers and must be fully enforced. Many low-paid workers only have the confidence to complain about underpayment after they have left."

Wednesday July 9 2003