Top civil servants across Whitehall are to be asked to draw up plans for how they would deliver personnel cuts of up to 40% in each of their departments, Sky News understands.
Two senior government sources have said the Cabinet Office is poised to write to all permanent secretaries asking them to model what would be required to slash staffing numbers in three different scenarios: cuts of 20%, 30% and 40%.
It follows a call from Boris Johnson for a 20% reduction in staff – 90,000 people – across Whitehall.
Sky News understands the decision to request modelling for cuts of up to 40% is to allow for some flexibility because some departments will be able to cut more than 20% and some less than 20%.
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One senior civil service source suggested demands of 40% cuts were likely to end up being more of a “sabre-rattling/theoretical exercise”, adding that it would be “pointless” because no department would be able to absorb such a reduction.
But senior figures say the prime minister, his chief of staff Steve Barclay and the chancellor are determined to press on with the demands.
Last week, the PM ordered ministers to come up with plans to cut more than 90,000 civil service jobs in order to free up billions of pounds for measures to ease the cost of living crisis with possible tax cuts.
During an away-day with cabinet ministers in Stoke-on-Trent, the prime minister asked them to report back within a month on how they could reduce the size of their departmental workforces to 2016 levels.
That would imply a reduction of about a fifth in the 475,000-strong workforce.
Details of the plan would be set out in due course, the government said.
It would be expected to save about £3.5bn a year.
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It comes as Mr Johnson faces pressure to do more to address the cost of living crisis, which has seen inflation soar to its highest level in three decades – with Tory MPs pressing for tax cuts and Labour accusing him of being “bereft of ideas”.
At the time of the original reports of the PM’s intention to shrink the civil service, a government spokesperson said: “The PM and ministers are clear that the civil service does an outstanding job delivering for the public and driving progress on the government’s priorities.
“But when people and businesses across the country are facing rising costs, the public rightly expect their government to lead by example and run as efficiently as possible.”
Jacob Rees-Mogg insisted the plans do not amount to the return of austerity.
Speaking to Sky News last Friday, Minister for Brexit Opportunities and Government Efficiency Jacob Rees-Mogg said the government is trying to get the civil service “back to normal” after taking on “extra people for specific tasks” including COVID-19 and Brexit.
Asked if reducing the number of civil servants constitutes a return to austerity, Mr Rees-Mogg said: “I don’t think it is because what is being done is getting back to the efficiency levels we had in 2016.”
He said the easiest way to cut staffing levels is “to have a freeze on recruitment”, as “up to 38,000 people each year leave the civil service”.
Mr Rees-Mogg continued: “The only bit that is ideological is that we should spend taxpayers’ money properly and not wastefully.
“It’s about doing things properly. It’s about governing effectively and recognising that every penny we take in tax has to come off the backs of people working hard.”
Amid the discussion on civil service efficiency, it was pointed out to Mr Rees-Mogg that he had arrived for his morning broadcast round alongside a handful of advisers.
Asked whether all were necessary, he said: “They don’t all work directly for me. They work within the Cabinet Office – and two are my special advisers.”