Police to be told not to confer before writing up notes.
Police officers in England and Wales are to be instructed not to confer before writing up their notes of serious incidents they are involved in.
Guidance will be issued to forces once it has been approved by the home secretary.
At present, officers can pool their recollections before making individual statements.
The draft guidance says conferring "has the potential to undermine public confidence".
In January, the BBC learned that the Independent Police Complaints Commission was preparing the new guidance which will apply to incidents in which someone dies or is seriously injured.
Now published in draft, it tells forces that police witnesses should be instructed not to speak, or otherwise communicate, about the incident in question.
They should be kept separate until after their detailed individual factual accounts have been taken, it says.
"Any conferring between witnesses has the potential to undermine the integrity of their evidence, and to damage public confidence in the investigation," it continues.
"As a result, non-police witnesses are routinely warned not to discuss the incident in question either before or after they have given their accounts.
"The same should apply to policing witnesses."
The guidance adds that if it is necessary for policing witnesses to discuss an incident "to avert a real and immediate risk to life", then "the extent to which such discussion has taken place, the justification for doing so and the content of that conversation, must be recorded as soon as possible".
BBC home affairs correspondent Danny Shaw said: "There's likely to be strong resistance from some officers, but concerns about public trust in policing are such that the IPCC may be pushing at an open door."
Following the 2008 shooting by police of barrister Mark Saunders, a High Court judge declared that conferring was an institutionalised "opportunity for collusion".
But he accepted that banning it could hinder investigations, and the practice continued.
After the shooting of Mark Duggan in Tottenham in 2011, however, officers involved wrote up their accounts in the same room, leading to renewed calls for a ban.
A public consultation on the new guidance will run until 27 May.