Tens of thousands of Scottish workers are threatened with pay freezes or even cuts under Tory-LibDem Government plans to revise the minimum wage.

Unions and opposition parties have reacted furiously to moves by the Coalition that could delay or scrap future increases in the rate.

But Downing Street insisted it was correct to look at any rises, saying ministers had to be sure the system works.

Just over 100,000 jobs in Scotland are thought to pay the minimum wage, which last year rose to £6.19 for over 21s and £4.98 for 18 to 20-year-olds.

But any cut in the rate, either in cash or real terms, would have a knock-on effect on the pay of thousands of other workers.

Labour condemned the move, attacking the Chancellor who yesterday said in a speech he wanted April to be the month in which the Coalition made sure "work pays".

Chris Leslie, Labour's Shadow Treasury Minister, said: "How can George Osborne claim he wants to make work pay when the Government is considering cutting or freezing the minimum wage? His speech will be exposed as totally empty rhetoric."

The Tories opposed the minimum wage ahead of its introduction by Labour in 1999, warning it would cost thousands of jobs.

Unite, the public sector union, yesterday warned freezing it now would damage the UK economy. The union's general secretary, Len McCluskey, said: "Cutting or freezing the minimum wage would make the struggling economy worse and create even more hardship for the lowest paid workers in Britain.

"The argument that the minimum wage harms the economy is utterly spurious."

But the move was defended by No 10. The Prime Minister's spokesman said: "We've always said on the minimum wage that it's important it works. It's something we are looking at. We need to make sure it works to support people."

The Low Pay Commission, which sets the minimum wage, has been told by ministers it has to consider any potential impact on the economy and employment before it agrees any future rate increases.

The commission estimates about 4.2% of the 2.5 million people employed in Scotland are in jobs that pay the minimum wage. The largest number of minimum wage jobs are found in the hospitality sector and retail, followed by social care, cleaning and hairdressing.

In his speech, Mr Osborne also attacked his critics for talking "ill-informed nonsense" on welfare reform.

The Chancellor has faced growing opposition from churches, unions and opposition parties, on a series of changes being introduced this month.

These include the so-called "bedroom tax" – a cut in benefit payments to council house tenants who have a spare bedroom.

But Labour seized on this month's reduction of the 50p tax rate to 45p. Ed Balls, Labour's Shadow Chancellor, said: "George Osborne should be straight with the British people and admit that millions on middle and low incomes are paying the price for his economic failure, while he gives a huge tax cut to millionaires this week."

Dr Eilidh Whiteford, the SNP's Westminster spokeswoman for work and pensions, said: "A freeze in the minimum wage, as living costs rise, would be another blow to some of the country's poorest people. Our lowest earners should not face the brunt of the Coalition's austerity measures."