The civil service will be tested to the limit by the demands of Brexit, with more officials likely to be needed to cope with the challenge, according to expert analysis.
A report by the Institute for Government (IfG) and the UK in a Changing Europe project stressed that as well as handling the Brexit talks, Whitehall would also need to prepare the UK for life outside the EU.
It is "inevitable" that there would be increased spending in ministries likely to see an increased workload after Brexit, such as the Home Office and the Department for Environment, Food and Rural Affairs (Defra), the report said.
Professor Anand Menon, director of UK in a Changing Europe, said: "The pressure of Brexit will be felt right across government and delivering it alongside existing commitments will test capacity to the limit.
"The civil service has many of the core skills required to do the task but effectively managing competing priorities and limited resources will require strong leadership."
IfG programme director Jill Rutter said pressure on the civil service will intensify as the countdown to exit starts once Theresa May has triggered Article 50.
She said: "With limited time and capacity, the pressure on ministers and the civil servants supporting them will increase. Successfully delivering Brexit in this context will require agility, leadership and realism."
The paper identified four key demands on the civil service: analysis, coordination, legislation and delivery.
Whitehall departments have been asked to prepare for Brexit on top of pre-referendum manifesto commitments, as well as continuing to implement budget cuts.
The report said it appeared some ministries had been given an indication that spending restrictions could be eased to help them cope with Brexit.
"In order to free up capacity for future stages of Brexit, departments need a steer from the Government as to what policies can be delayed or dropped.
"In other areas, the amount of work is such that reprioritisation alone will not work - it appears inevitable that the Government will have to revise the spending plans of departments such as Defra and the Home Office.
"The fact that key affected departments are already recruiting shows that they must have been given indications that they will not be held to the administrative savings agreed in the pre-Brexit spending review."
The report also highlighted the need for Government lawyers to be prepared for last-minute changes to legislation
It said: "In order to prevent a period of legal and regulatory uncertainty, the Government will produce a Great Repeal Bill, transposing EU laws into the UK statute book.
"It must ensure that there is sufficient capacity in the Government Legal Service and parliamentary counsel, and in Parliament itself, to allow necessary legislation to be prepared, scrutinised and approved before the UK leaves the EU.
"As the end of the two-year negotiating window approaches, government will need to retain enough capacity to manage last-minute changes and adapt to any deal that is made."
Jon Trickett, shadow minister for the Cabinet Office, said: "Brexit will put a lot of pressure on an already cut-back civil service. The Government is taking a gamble with the country's future if it doesn't equip their staff adequately.
"When they've been subject to a continuing pay freeze, shrinking budgets and low morale, public servants need to become a priority for Theresa May if she wants to avoid any more risks with Brexit.
"The dangers to our country are clear and the Prime Minister should listen to the warnings. She needs to stop this recklessness and provide a well-run civil service for the good of the whole country when we leave the EU."
A Cabinet Office spokesman said: "The civil service is well equipped to deliver all of this Government's priorities, including the UK's exit from the EU.
"Civil servants have shown resilience and adaptation on countless occasions to major challenges and critical work. We have the right skills, experience and leadership to help achieve the best deal for the UK."