The head of Britain’s leading independent economic think tank has launched a scathing attack on Rachel Reeves, describing tax rises in her Budget as ‘ridiculous’.

Paul Johnson, chief executive of the highly influential Institute for Fiscal Studies (IFS), said his head ‘literally hit the table’ when the Chancellor announced a stamp duty increase and a winter fuel duty freeze.

Johnson and the IFS are respected by politicians on all sides for their impartiality and the quality of their analysis.

He was described this weekend as the ‘financial arbiter of Westminster’ and ‘the thinker’s financial collaborator’ in recognition of the unique role he plays in Britain’s political system by analyzing the Budget and preventing any ‘spin’.

All politicians are eager to get his approval, so his outspoken comments on the Budget will hit Reeves hard.

“I did not foresee the increase in employer national insurance contributions,” he said in an interview with the Times. ‘I understood the manifesto to exclude this.’

Johnson added that stamp duty was ‘the most damaging tax we have’ and warned that increasing it would only ‘immobilize businesses further and raise rents further’.

He said the Chancellor’s decision against increasing fuel taxes was ‘ridiculous’.

Paul Johnson, chief executive of the prestigious Institute for Fiscal Studies (IFS), said Rachel Reeves’ head ‘literally hit the table’ after her ‘ridiculous’ budget

Reeves was accused this weekend of underestimating the economy as new figures revealed growth was slowing.

Data from the Office for National Statistics showed gross domestic product grew by just 0.1 per cent in the three months to the end of September.

Critics blamed the Chancellor for the slowdown in his first three months in office, saying he had underestimated the economy, leaving businesses and households hesitant to spend.

Once in power, the Chancellor repeatedly insisted that the economic legacy from the Conservatives was the worst economic legacy for any new government since the Second World War.

Business groups have warned Reeves will make matters worse following his move to increase employers’ national insurance contributions in the budget. Analysts predict it will raise £25bn and could cost 100,000 jobs.

Critics blame the Chancellor for a slowdown in his first three months in office and say he has underestimated the economy

Shadow Chancellor Mel Stride said: ‘I fear they are being rewarded to some extent for what they have done in terms of collapsing the economy.

‘And of course what they’ve done now is to follow that up with a Budget that increases taxes, particularly taxes that will impact growth.’

Johnson is also skeptical about the long-term strength of the UK economy, with an aging population the biggest challenge facing the country.

He said: ‘Pensions, social care and health spending will increase.

‘If we don’t want to tax or borrow more, something else is going to have to come down. We need to decide what will happen.’