The Cabinet Secretary, Sir Jeremy Heywood, has said spending cuts could continue until 2020, according to sources at a well-known think-tank.
The top civil servant is reported to have made the comments at an event at the Institute for Government mostly attended by civil servants.
He was discussing the coalition’s civil service reform plan.
The government has already announced the austerity programme would continue beyond the next election.
But the suggestion of an eight-year timescale has not been talked about openly, says BBC political correspondent Iain Watson.
On Tuesday, Cabinet Office Minister Francis Maude announced a package of reforms to the civil service, which included plans to make it easier to sack under-performing staff members.
Mr Maude said he wanted to see the civil service operate more like a business, with a tougher appraisal system, increased accountability and a more entrepreneurial culture.
The planned changes come against a backdrop of deep cuts and job losses across Whitehall.
Sir Jeremy – who, along with head of the civil service Sir Bob Kerslake, will lead the implementation of the reform plan – told an audience at the Institute for Government the UK was only 25% through its fiscal adjustment and spending cuts could run for “seven, eight, maybe 10 years” from when the coalition came to power.
The cabinet secretary talked about a programme of reform in the civil service which could last 10 years and lead to a less hierarchical structure.
The Cabinet Office said: “Jeremy was simply saying that financial pressure would continue into the next parliament.