Boris Johnson has been warned to “tread carefully” amid claims Number 10 aides are asking civil servants to operate an “overtly political” Brexit media strategy.

A Cabinet Office document leaked to HuffPost UK has revealed all government communications staff must report “unhelpful narratives” in the press and online to Downing Street.

While civil servants work for the government and are expected to ensure ministers can deliver on policy, they also have a duty to be impartial.

The document is further evidence suggesting Johnson’s most senior adviser Dominic Cummings – the ex-boss of Vote Leave once described by David Cameron as a “career psychopath” – is prepared to introduce sweeping change in order to deliver Brexit by October 31.

The controversial advisor is reported to have already had a huge impact on Number 10 since arriving last month, embarking on a so-called “jihad on spads [special advisers]” by cancelling annual leave and sacking aides from the Theresa May era.

According to the document, staff have been instructed to update Downing Street from 6am each morning with “all rebuttal lines to be approved by Number 10”.

The unit must also “counter emerging narratives” and ensure all departments push the Downing Street line, adding “if action not completed, escalate as needed”.

Shadow Cabinet Office minister Jon Trickett said Boris Johnson was “playing with fire”, adding: “Political neutrality is a central principle which has endured in relation to civil servants for more than 150 years.

“It is essential that the present government does not breach this basic part of the constitution. To do so would further imperil faith in politics, which is already at a low ebb.”

Alastair Campbell, who acted as former PM Tony Blair’s communications chief, called on civil servants to keep a record of “overtly political” requests.

Dave Penman of the FDA union, which represents senior civil servants, has also warned Johnson he risks “politicising” the work of his members.

Downing Street said it would not comment on leaked documents.

A source, however, stressed that the guidance was issued by the Cabinet Office and the Department for Exiting the EU, not Number 10, and was part of a standard cross-government communications plan.

But Campbell said: “There is a clear division between the legitimate work civil servants must do in support of ministers implementing government policy and this overtly political work which they are being asked to do.

“Clearly Johnson and his team wish to see that division straddled.”