Police officers directly involved in fatal incidents should be separated as quickly as possible to prevent conferring, a watchdog has said.
The step is included in new guidance from the Independent Police Complaints Commission (IPCC) on how evidence should be collected immediately after a member of the public has died or been seriously injured during contact with the police.
Key policing witnesses should be separated as soon as it is "operationally safe" until after they have provided their personal initial account, according to the document.
The IPCC said separating officers after an incident to prevent conferring is designed to ensure officers provide individual accounts of what they themselves saw, heard and did.
This avoids actual or perceived collusion or their accounts being unintentionally influenced by those of others, the watchdog added.
It stressed that this should happen only once it is operationally safe. For example, during an ongoing terrorist incident, the police operation takes precedence and any separation of officers would wait until the risk to life had passed.
The issue of conferring among officers has come under the spotlight following high-profile cases, including the fatal shooting of Mark Duggan in 2011.
The new guidance also says policing witnesses should provide personal initial witness accounts before they go off duty, while they should not view their own body-worn video before offering their initial account.
IPCC Deputy Chair Sarah Green said: "A critical role of the IPCC is to investigate deaths or serious injuries following contact with the police.
"We investigate with an open mind, so it's vital that we get the best evidence from police witnesses as quickly as possible, which in turn helps promote public trust in the process.
"We have proposed fresh guidance to help us achieve that aim.
"The measures we have outlined do not treat police officers as suspects, but as witnesses whose early individual accounts will help ensure the integrity and smooth running of the critical early stages in any investigation.
"It's in everyone's interest that the process for gathering evidence is swift, clear and transparent. It helps the public have confidence that police actions are independently scrutinised.
"It speeds up our investigations, which is precisely what the police, bereaved families and complainants want."
If approved by the Home Secretary, all police forces in England and Wales will be obliged to make use of the new guidance in the event of fatalities or serious injuries resulting from firearms operations, incidents in custody or other police contact.
Che Donald, firearms lead for the Police Federation of England and Wales said: "Officers absolutely understand the spotlight they face following a death or serious incident and are under no illusion that there will be scrutiny of decisions made, and rightly so.
"However, this has to start on the right foot. They are witnesses first and foremost and to separate them in the immediate aftermath of a highly traumatic incident is neither proportionate nor necessary and without cause."