The Cabinet Office will cut 400 jobs as part of reforms to cut red tape and remove duplication of roles.

The job losses, amounting to around 6% of the department’s 6,315 staff, will be achieved through a voluntary exit scheme, the Cabinet Office’s senior official Cat Little told civil servants on Thursday.

The move comes with more than 10,000 jobs thought to be at risk across Whitehall departments due to a squeeze on government spending.

We are reforming the way the Cabinet Office works, moving to a smaller, clearer structure

The Cabinet Office changes are aimed at creating a “smaller, clearer structure” for a department which works across a whole range of government functions.

A Cabinet Office source said: “To deliver meaningful change across the civil service and the country the Cabinet Office needs to have an even more strategic role at the centre of government.

“Over the years, it has been asked to do more and more – as a result it has lost its focus. We have a rare opportunity to refocus the Cabinet Office on what only it can do – we must not miss this genuine opportunity for reform.”

The Cabinet Office is responsible for supporting the Prime Minister in the effective running of government but its remit covers areas ranging from Civil Service reform to intelligence and national security, and it works closely with No 10.

A Cabinet Office spokesman said: “We are reforming the way the Cabinet Office works, moving to a smaller, clearer structure.

“Our strategic plan will remove duplication and unnecessary bureaucracy, empower teams and individuals to be creative and innovative in their work and improve the delivery of Cabinet Office core activities.

“We will create a smaller, more effective Cabinet Office that can coordinate delivery across government under the plan for change.

“Throughout the process we will engage with staff on any changes made.”

The move from the Cabinet Office followed reports that departments may seek to axe thousands of jobs after being told to find 5% efficiency savings in their budgets by Chancellor Rachel Reeves.

The size of the Civil Service has increased from a low of around 384,000 in mid-2016 to more than 510,000 and the Tories went into the general election promising to reduce numbers by 70,000 to fund extra defence spending.

Any reduction under Labour would be more modest, with the Guardian reporting more than 10,000 jobs could be lost although there is no set target.

A Government spokesman said: “We are committed to making the Civil Service more efficient and effective, with bold measures to improve skills and harness new technologies.”

Mike Clancy, general secretary of the Prospect trade union said: “We need a clear plan for the future of the civil service that goes beyond the blunt headcount targets that have failed in the past.

“This plan needs to be developed in partnership with civil servants and their unions, and we look forward to deeper engagement with the government in the coming months.”

A Government source said: “The number of civil servants cannot keep growing. But we will not set an arbitrary cap.

“The last government tried that and ended up spending loads on more expensive consultants.”