The number of civil servants working in central London "will reduce significantly" over the next few years, the Treasury has said, as the government eyes a move to the suburbs for many officials.
Under plans outlined by ministers earlier this year, the number of buildings occupied by government departments is set to fall sharply, from 800 to under 200 by 2023.
Departments will increasingly be expected to share office space under a plan for so-called "Government Hubs", which the Cabinet Office has said will enable "easier cross-departmental collaboration as well as having important benefits for recruitment and retention".
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Wednesday's Budget highlights ongoing efforts to reduce the government's central London footprint, which is expected to shrink from more than 50 sites today to around 20 by 2025.
The Treasury said: "The government is working on an ambitious strategy to move civil servants out of expensive Whitehall accommodation and into the suburbs of London, delivering substantial savings for the taxpayer. Over the next few years the numbers working in central London will reduce significantly."
Meanwhile, the Budget says the Ministry of Justice is working on "a major programme to create substantial centres of expertise outside the capital" by the middle of the current parliament, which it said would involve "moving jobs out of Whitehall".
"This will reduce costs, access highly skilled labour markets in the regions and contribute to the Northern Powerhouse," the Treasury added.
The MoJ announcement came as chancellor George Osborne told MPs that department was preparing to hand "new powers over the criminal justice system" to Greater Manchester, as part of the government's wider decentralisation agenda.
"This is the kind of progressive social policy that this government is proud to pioneer," he added. The Greater Manchester Combined Authority is already set to gain powers over transport, housing, planning and policing after agreeing to have a directly-elected mayor.
The location of civil servants has been the subject of some political controversy in recent weeks, with Labour highlighting that just 2.4% of senior civil servants at the Department for Communities and Local Government – which leads on the government's devolution deals – work outside of the capital.
The opposition has also pointed out that 99.9% of the Treasury's core policy civil servants work in London – although the finance ministry on Wednesday dismissed those figures as "totally misleading".
A Treasury spokesperson added: "The whole point of the devolution revolution is to take powers away from Whitehall – and next year more than half of the northern powerhouse will be covered by an elected mayor. This is the biggest shift in the way Britain is governed for a generation."
Meanwhile, the planned closure of the Department for Business, Innovation and Skills' site in Sheffield has sparked the ire of local MPs, and the PCS union is considering industrial action in response to HM Revenue and Customs' own proposals to reduce its estate from 170 sites to just 13 regional centres.
According to the latest statistics, 18.1% of the total civil service workforce was based in London in September 2015, a 2.8% increase on the previous year