Unauthorised leaks by ministers and civil servants will soon result in instant dismissals - a leaked memorandum has revealed.
Theresa May ordered the crackdown in a bid to tighten security at Whitehall, cabinet secretary Sir Jeremy Heywood revealed in a letter to senior officials.
But somewhat ironically, the Prime Minister's plans were leaked to The Mail on Sunday just days after they were issued.
In his note - dated November 28 and marked Official-Sensitive - Sir Jeremy referred to a "spate of leaks and unauthorised briefings" which had appeared in the media on Brexit, the US elections and the Autumn Statement.
Sir Jeremy wrote: "Leaking is corrosive and undermines 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.
"The Prime Minister has directed that we urgently tighten security processes and improve our response to leaks.
She has instructed that we begin this work immediately and expects to see rapid and visible improvement.
"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.
"If leaders think they are the necessary cost of open ways they are mistaken".
He concluded: "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".
Downing Street has declined to comment on the Mail's report.