Brexit is being blamed for record levels of staff turnover in the Cabinet Office, with more than one in three civil servants leaving the Whitehall department each year.
Cabinet Office churn soared from 20% in 2010 to 35% in 2016, according to recently released figures.
This is almost four times the average staff turnover rate of 9.1% across the civil service.
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The rise reflects a growing need for "short and medium term expertise to be brought in from other government departments, parts of the public sector and from outside the public sector to work on changing priorities over specific periods of time," according to Cabinet Office minister Ben Gummer.
In a written statement to MPs last month, responding to a parliamentary question from shadow Cabinet Office minister Jon Trickett, he added: “Increasing use of fixed term appointments in recent years and, in the last year the transfer out of a large number of staff to the Department for Exiting the EU, means that turnover has been high.”
The rising staff turnover at the Cabinet Office is part of a wider trend across Whitehall departments.
Churn at the Department for Environment, Food and Rural Affairs, at 22%, is more than double the level it was in 2010.
While staff turnover at UK Export Finance increased from 6% in 2010 to 21% in 2016.
Other departments with high turnover include the Wales Office (36%); HM Treasury (19.5%); the Department for Education (13%); and the Ministry of Justice (12%).
Commenting on the figures, Trickett told CSW: “Over recent years we have seen worryingly high turnover rates of staff in several governmental departments, including the Prime Minister's office which has one of the highest rates of churn. The loss of up to a third of staff each year points to a concerning lack of skills retention in the civil service.”
“As we leave the EU, we need a civil service with the long term capability that will help to deliver a clear plan for the future,” he said. “It is crucial that we understand why so many public servants are leaving their positions.”
The Labour MPs concerns were echoed by a spokesperson for the FDA union who said: “Turnover inevitably means losing institutional memory, which could create additional workload as others struggle to fill the gap. Additionally, valuable skills and experience can be lost, which can be particularly hard to replace if these skills are prized in the private sector and there is a competitive pay market.”
In a statement, a government spokesperson said: “We actively encourage civil servants to move roles, sectors and departments to allow for a broad range of career paths and experiences, ensuring the right skills are available to deliver the Government's priorities – including leaving the European Union.”
They added: “Retention of employees across the civil service remains high, while the civil service engagement index is currently at its highest recorded level.”