Theresa May has called for urgent action to prevent ministers and government officials from leaking information about the Brexit process to journalists.

The prime minister’s demand resulted in a warning memo from the cabinet secretary that, ironically, was itself passed on to a national newspaper within days.

Sir Jeremy Heywood wrote to permanent secretaries in government departments to say that a “spate of corrosive leaks” must end.

He said there was a need for a “cultural change”, and set out plans to review areas vulnerable to leaks and to place security teams in charge of ramped-up inquiries into who was passing information on.

“Anyone found to have leaked sensitive information will be dismissed, even where there is no compromise of national security,” he said.

Heywood also wrote: “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 of working they are mistaken.”

Heywood also revealed that he had strengthened control for “sensitive cabinet committee papers” that were used by senior members of May’s team to discuss Brexit plans so far.

In October, the Guardian revealed that one of the papers Heywood referred to had warned cabinet ministers of a 4.5% drop in GDP by 2030 if Britain withdrew from the customs union.



It followed a leak that another of the reports had included a controversial figure used during the referendum that said hard Brexit could cost £66bn a year, and that the government was looking at a migration system under which people could only come to Britain for a specific job.

Downing Street would not comment on the leak, but did not deny that it was genuine.

The former Labour cabinet minister Ed Balls suggested that the document reminded him of his time working under Gordon Brown’s premiership.

“I have seen these memos in the past – they happen when a prime minister is losing grip … the prime minister needs to show leadership,” he said on ITV’s Peston on Sunday.

The document shines a light on the frustrations in the government over leaks thwarting its attempt to maintain “no running commentary” around the Brexit process.

However, the vacuum that has been left means any revelation is pored over by the press. One handwritten note, photographed when the aide to a senior Conservative MP carried it on Downing Street, suggested Britain would have to leave the single market.

The notes, which were presumed to have been written during a meeting with officials or ministers in the Department for Exiting the EU, also included: “What’s the model? Have cake and eat it,” and suggested: “French likely to be most difficult.”