A Scotland Yard riot squad officer filmed knocking Ian Tomlinson to the ground will be told tomorrow if he faces prosecution over his death.
Keir Starmer, Director of Public Prosecutions, will reveal whether the officer has a case to answer over the G20 protest clash.
The officer, a member of the force's controversial territorial support group, was caught on camera pushing the newspaper seller to the ground.
Mr Tomlinson, 47, died from internal bleeding after collapsing a short distance away in the City of London on April 1 2009.
Members of the Tomlinson family will be told the decision at the headquarters of the Crown Prosecution Service (CPS) at around 11am.
The decision, made on the fifth anniversary of the death of Jean Charles de Menezes, is likely to spark controversy, whether the officer is prosecuted or not.
Campaigners have already said they will gather outside New Scotland Yard to protest against police violence two hours after it is made.
No British police officer is thought to have ever been convicted for manslaughter committed while on duty. The maximum penalty is life imprisonment.
The officer, who remains suspended from duty, could be charged with manslaughter, assault, misconduct or told no further action will be taken.
Mr Tomlinson's death became global news after amateur video evidence emerged that challenged the original official version of events.
Police told his widow and nine children he died of a heart attack after being caught up in crowded streets around the protests.
But the footage showed Mr Tomlinson being struck from behind by a baton and shoved to the ground by an officer in protective clothing.
He was found several minutes later about 100 metres away collapsed on the ground in Cornhill.
Prosecution solicitors have examined the video footage as well as CCTV images, photographs and witness statements.
Three post-mortem tests were conducted on Mr Tomlinson's body leading to different conclusions.
The first found he died of natural causes, the second of internal bleeding and the results of the third, conducted on behalf of the officer, were not made public.
In recent months, the Tomlinson family has criticised the CPS for taking too long to reach a decision.
The Independent Police Complaints Commission completed a criminal inquiry last August and handed over a file of evidence.
Green politician Jenny Jones, a member of the Metropolitan Police Authority, said the decision was "crucial for the reputation of police everywhere".
She said: "The recommendation by the CPS on Ian Tomlinson provides a key test of how well our justice system deals with aggressive policing.
"People don't want scapegoats, but they do need to know that the police are not above the law. This is an issue of public confidence.
"If the police behave unprofessionally, then they should be disciplined. If the police appear to assault someone, then that is rightly a matter for the courts."Reuse content