Last year, the Trade Unions Congress produced analysis which estimated that in 2024 3.8 million people worked an average of 7.2 unpaid hours a week, losing out on earnings of £8,000 per year.
The body said those in the teaching and health and care jobs were most likely to be working unpaid hours.
Treasury Chief Secretary Lucy Rigby said: “If Reform want people to take their unfunded, back-of-a-fag packet plans seriously, they should come clean about where their £40bn of cuts would fall and which public services would pay the price.”
Shadow chancellor Sir Mel Stride said: “Hard work should be rewarded, which means getting taxes down in a fair and responsible way. Reform’s proposal sets out no new savings… they keep promising things they cannot deliver.”
Liberal Democrat deputy leader Daisy Cooper said: “Farage’s fantasy economics is a gamble our country cannot afford to take. The Liberal Democrats are the only party that used its opportunity in power to raise the income tax threshold taking millions of people out of paying tax altogether.”
Helen Miller from the Institute of Fiscal Studies said the Reform proposal was “problematic in principle and practice”, and “if the intention is to increase labour supply, it is not clear why an incentive should be targeted at increasing the hours of employees already working at least 40 hours a week”.
Miller said it could also create an incentive to have more work classified as “overtime” in order to reduce tax payments, adding “evidence from a similar French policy is not encouraging”.