A Scotland Yard officer faces a gross misconduct inquiry for writing a book voicing concerns over police reforms.
Whistleblower Pc James Patrick has been placed on restricted duties after he aired fears relating to funding cuts and privatisation.
The officer, who has nearly 3,000 followers on Twitter where he has addressed the same issues, has reportedly been told to cease communicating with the public, an order which effectively bans him from the micro-blogging site.
His 426-page book, The Rest is Silence, promises the "fully documented" background to police reform and the G4S fiasco at the Olympics, along with a "detailed exploration of the next political scandal waiting to happen: think tanks and ministers".
Pc Patrick's lawyer Karen Todner told The Guardian: "He is a whistleblower and what this is about is freedom of expression. This is someone who has tried to raise his concerns through the legitimate channels but was not able to do so."
Pc Patrick last posted on Twitter three days ago, writing: "If anyone has any scaremongering or baseless hysteria related queries, please direct them appropriately. Thank you and see you soon."
He was placed on restricted duties on Friday and is subject to an inquiry by the Met's Directorate of Professional Standards.
Scotland Yard said it was "not standard practice" for serving police officers or members of police staff to be allowed to write a book about their work but permission could be granted in "exceptional circumstances".
A spokesman said: "A serving police constable, currently based within territorial policing, will be subject to gross misconduct proceedings."
The Rest is Silence is available on Amazon priced £15.99.