ALL large businesses across Britain, including almost 500 in Scotland, will within the next 12 months have to publish the difference in average pay for their male and female workers.

The Liberal Democrat leadership hailed the breakthrough on gender pay transparency as a major triumph for the party, which recommended it in its 2010 election manifesto.

Lib Dem sources said the party had finally forced the Tory leadership to back the move after dragging its heels on the issue for the last five years, which meant it was now set to get through parliament before the General Election.

"This is extraordinary on International Women's Day when you have some Tories feigning support for women in the economy while dragging their feet on gender pay transparency," declared one source.

"It's a huge U-turn from the Tories but it's welcomed."

The Liberal Democrats have argued for mandatory pay transparency since the Coalition was formed but, in the wake of Conservative opposition, agreed to an initial voluntary approach.

But it has emerged that just five companies have chosen to publish their gender pay gap voluntarily.

The new policy will not apply to firms with fewer than 250 employees. In Scotland, 490 firms, employing more than 630,000 workers, will be affected.

Nick Clegg, the Deputy Prime Minister, said: "It simply cannot be acceptable that, in the 21st century, women on average still receive a smaller pay packet than men. We can't wait and we can't dither. We need to sort this out now."

His Lib Dem colleague, Jo Swinson, the Women & Equalities Minister, stressed how it was thanks to the Liberal Democrats in government that changes to help achieve equal pay for women in Scotland were being made.

"Over 40 years on from the Equal Pay Act, our labour market is still stacked against women when it comes to pay. A woman is still paid on average 20 per cent less than a man and less likely to be in a leadership role."

Ms Swinson, who represents East Dunbartonshire, added: "There are 490 large Scottish businesses employing 633,000 people. Forcing large companies in Scotland to publish the difference between average pay of men and women will mean, for the first time, we will have public information on the gender pay gap."

The move on pay will come in an amendment to the Small Business Bill, due to be debated in the House of Lords next week. The Lib Dems said all those on the Government payroll will vote for the change.