The decision not to prosecute Pc Simon Harwood over the death of Ian Tomlinson will not alter, the Crown Prosecution Service has said.
Mr Tomlinson died after he was pushed at the G20 protests in April last year.
The Director of Public Prosecutions, Keir Starmer QC, reviewed the decision after the suspension of pathologist Dr Freddy Patel.
Dr Patel had carried out a post-mortem on Mr Tomlinson but was later suspended over unrelated matters.
The DPP said there was "no realistic prospect" of conviction whether Dr Patel is called as a witness or not, according to the BBC's Danny Shaw.
Mr Tomlinson had been on his way home from work during the protests and was not involved in the demonstrations.
Pc Simon Harwood, a member of Scotland Yard's territorial support group, was filmed striking the 47-year-old newspaper seller with his baton and pushing him to the ground in the City of London.
No criminal proceedings were brought over Mr Tomlinson's death because experts could not agree on how he had died.
Following the findings by the General Medical Council on Dr Patel's fitness to practise, Mr Starmer has published a letter he sent to Jenny Jones, a member of the Metropolitan Police Authority.
He wrote: "It is important to appreciate that it was not the sharp disagreement alone that caused the CPS to conclude that no prosecution for manslaughter could be brought."
These, according to Mr Starmer, included the difficulty concerning "the source of the internal bleeding" and the fact that Dr Patel had discarded three litres of fluid taken from Mr Tomlinson's body, without having analysed it.
In July, Mr Starmer said there was a "sharp disagreement between the medical experts" about the cause of death.
Dr Patel, who has since been suspended from the medical register over three other cases, concluded that Mr Tomlinson died of natural causes.
However, two other experts said he died from internal bleeding after falling to the ground.