It is understood that Ms Reeves is considering limiting the National Insurance relief scheme to £2,000 per annum for both staff and employers’ contributions to pensions.

However, the Daily Telegraph revealed that the government has no idea how many workers are actually on such schemes, and therefore does not know how many people will be affected by the proposed change.

Sarah Olney, a Liberal Democrat MP and their spokesman on Business, asked Ms Reeves to confirm what information the Treasury has on workers making use of salary sacrifice schemes.

She was informed by the Treasury Minister Dan Tomlinson MP that: “HMRC does not hold administrative data on the number of employers offering and employees using salary sacrifice schemes.”

The changes mean that millions of British workers are set to lose money to line the Treasury’s coffers as part of a Budget that is rumoured to send taxes skyrocketing.

During the general election, Labour politicians made repeated promises not to raise National Insurance, Income Tax or VAT.

Ms Olney told the Telegraph: “It’s outrageous that Rachel Reeves is planning to tax salary sacrifice schemes without having any idea how many people her decision will impact. As if we needed more reasons not to trust this Treasury.

“It will be a kick in the teeth to the millions set to tighten their belts this winter that the Government is playing so fast and loose with their savings.

“This afternoon the Chancellor must choose to fill the hole in the public finances by fixing our broken relationship with the EU, rather than crippling those already hit by a cost-of-living permacrisis.”

Andrew Griffith, the shadow business minister, said: “Businesses have long suspected she is making decisions without understanding the numbers – but it is still a shock to have this confirmed.”