The new chief executive of the civil service has said the government has tried to carry out "too much transformative change" at once.
Former BP executive John Manzoni told MPs that the civil service was having to do "30% too much across the board".
While it was their duty to implement government policy, he said "we have to be clearer about where it is possible and where it is impossible".
"We sometimes get sucked into things which are very difficult to achieve."
Mr Manzoni, who has been in the newly-created job for a month and first joined the civil service in February, said his objective in his new job was to "improve execution across government".
Making his first appearance before the Commons Public Accounts Committee since being appointed, he said the civil service had always been over-extended but the situation had become acute in recent years.
"We are doing 30% too much across the board, we always have been," he said.
"We have got too much activity. No company would undertake the level of transformative change that this government has. No company would do this."
'Promising the earth'
Mr Manzoni, who was previously head of the Major Projects Authority, said it was the civil service's function to "undertake the wishes of the government of day" while not "promising the earth" and ensuring changes were delivered in the most efficient way to ensure ministers' primary objectives were met.
There was no easy way to address the current situation, he suggested.
"We have to stop people having great ideas and everybody saying yes to them."
In his largely administrative role, Mr Manzoni - who said he had "no value" to add to policy development - will report to the Cabinet Secretary Sir Jeremy Heywood.
The roles of cabinet secretary, the most senior civil servant in Downing Street, and civil service head were split in 2012 but were consolidated following the recent retirement of Sir Bob Kerslake.
Mr Manzoni said the job was "much more challenging" than running a multinational company, since a company chief executive would "control the entire agenda" while Whitehall was a lot less centralised and the "exogenous" environment changed more.
He conceded, in his role, that none of the most senior civil servants in individual departments would report to him but he insisted he had "30 years' experience of delivery" and was confident he could improve the way government worked.
Mr Manzoni's former boss at BP, Lord Browne, recently resigned from his job appointing business leaders as non-executive directors of government departments.