Sir Jeremy Heywood has written to Whitehall's permanent secretaries to warn of tough action to combat a "spate of corrosive leaks" from government departments in recent months, as the trade union representing senior officials called for ministers to face the same threat of dismissal.
A note by the cabinet secretary – obtained by the Mail On Sunday and reportedly marked "official sensitive" – says a series of unauthorised leaks on issues including the UK's exit from the European Union, the election of new US president Donald Trump, and November's Autumn Statement threatened to undermine "trust and good government".
"Leaks are never acceptable but the regularity and cumulative impact of recent incidents mean we must now collectively take exceptional action," he wrote.
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Heywood said prime minister Theresa May had ordered the government to "urgently tighten security processes and improve our response to leaks" – and made clear that there would be a zero-tolerance approach to leaking.
"Ministers, permanent secretaries and senior officials set the tone in an organisation and no amount of process will make up for an environment where leaks are accepted," the head of the civil service wrote. "If leaders think they are the necessary cost of open ways they are mistaken."
He added: "Anyone found to have leaked sensitive information will be dismissed even where there is no compromise of national security. The prime minister will be writing in similar terms to ministers."
The Civil Service management code, which outlines the terms and conditions of civil servants' employment with the government, already makes clear that leaks are forbidden.
The code states that civil servants must not "disclose official information which has been communicated in confidence within government, or received in confidence from others".
Among the measures for strengthening oversight of leaks suggested in the memo are a redoubling of efforts to ensure only "official technology" is used for communications, with Heywood saying departments will need "to obtain phone and email logs quickly" and ensure staff are rapidly made available for interview when suspected of leaking. There will, he promises, be "tough disciplinary measures when a culprit has been identified to show leaking will never be tolerated".
Heywood added: "I have already strengthened the controls for sensitive Cabinet Committee papers. This will require all the energy and attention any cultural change demands."
Dave Penman, general secretary of the FDA union, said ministers must also face the same consequences as top officials if found to be leaking information.
“Ask any journalist worth their salt and they'll tell you that the vast majority of leaks emanate from politicians," he said.
"Indications have been given that the prime minister will issue a parallel and similarly robust statement outlining that any politician found to have leaked will face a similar sanction. This would be both welcome and appropriate.
“Civil servants are being threatened with the loss of their livelihood if they are caught leaking. A similar sanction should apply to politicians, not simply the loss of the trappings of ministerial office.”