Four out of five civil servants should be at their desks for some of the week by October, a letter from the UK's top mandarins has said.
Bosses of English government departments have been told the government is "now strongly encouraging" increased workplace attendance by the end of this month, in a bid to get those working for the state to return to their offices.
Many have been working from home as a result of the coronavirus crisis.
But the move has been criticised by unions, with one saying it is not practical and an example of "virtue signalling", and another threatening to explore legal or strike action.
It comes after criticism that not enough civil servants have returned to work in their offices.
This is because businesses that rely on them for an income are being hit hard, younger staff members are not receiving training and politicians' ability to implement policies is potentially being affected.
The letter, written by outgoing cabinet secretary Sir Mark Sedwill and Alex Chisholm, the chief operating officer, says: "We all recognise that this experience has been challenging for individuals and for departments.
More from Politics
"There have been challenges bringing on board new or inexperienced colleagues and limitations in the ability to mentor and develop our people.
"This is reportedly most acute for people without easy access to high quality home working facilities.
"Departments which are still below their departmental constraints should now move quickly to seek to bring more staff back into the office."
The issue affecting civil servants is the same for office workers and some employees in other sectors, with recent mobile phone data showing that only about 17% of UK workers had gone back to the office.
The Confederation of British Industry has warned that UK city centres face becoming "ghost towns" if people do not return to their workplaces soon.
Sir Mark said departmental permanent secretaries – which run government departments – should enable "80% of staff to attend their usual workplace each week, for example 20% for five days, 30% for three days and 30% for two days, with the balance attending only occasionally for now".
But the general secretary of the FDA, a union representing civil servants, said such targets would be difficult to achieve.
Dave Penman said office use in Whitehall was already "oversubscribedRead More – Source