As Britain bids to slash a record budget deficit, departments had been warned to expect spending cuts of about 25 per cent, but many ministries have now been asked to identify here cuts of 40 per cent could be made.
It is the latest step in laying the ground for a spending review to be published in October which is expected to be the toughest since World War II.
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The newly created Office for Budget Responsibility has forecast that 600,000 public sector jobs will be lost as Prime Minister David Cameron's Conservative-Liberal Democrat government grapples with the deficit.
Chancellor of the Exchequer George Osborne said last month that the defence and education ministries would receive favourable treatment, but they have now been told to assess the potential impact of cuts of 10 per cent and 20 per cent.
The only departments to escape any cuts will be health and international development, whose funding is "ringfenced" during the current parliament term.
A Treasury spokesman said: "We are determined to tackle the record budget deficit in order to keep rates lower for longer, protect jobs, and maintain the quality of essential public services.
"The Cabinet has been briefed on the planning assumptions that their departments should use for the initial phase of the spending review.
"These planning assumptions are not final settlements, and do not commit the Treasury or departments to final settlements.
"These assumptions will be negotiated so that we both tackle the deficit and support the freer, fairer and more responsible Britain we want to see."
