Senior MPs said there must be "zero tolerance" of racism in the police following the disclosure that an officer had been suspended for allegedly racially abusing a suspect during the London riots.
There was shock and anger after it was reported that the officer - named by sources as Pc Alex MacFarlane - told the 21-year-old black man:
"The problem with you is you will always be a nigger, yeah?
"That's your problem, yeah."
The chairman of the Commons Home Affairs Committee Keith Vaz said he was "deeply concerned" at the way the case was handled after the Crown Prosecution Service (CPS) originally decided not to bring charges.
According to The Guardian, the suspect was able to record the remarks on his mobile phone as he was being taken into custody by the Metropolitan Police officer on August 11 last year.
After receiving a file about the incident from the Independent Police Complaints Commission (IPCC), the CPS initially decided not to charge Mr MacFarlane and two other officers who were allegedly involved.
However last night the CPS said that it would look again at the case following a complaint from the detained man's lawyer.
Mr Vaz said that it was now essential to establish exactly what had happened.
"I am deeply concerned by these allegations and the way in which they have been handled," he said.
"We must establish the facts as to what actually occurred on August 11. However what I have heard suggests that lessons of the past have not been learned.
"If we are to have a police force that is trusted by its public, it has to be trusted by all people irrespective of their race. There must be zero tolerance towards the type of behaviour alleged in this case, not just by the perpetrator but also anyone who observes racist behaviour and does not stop it.
"This is not just a matter of potential criminality, this is a matter of standards and ethics."
Grace Ononiwu, deputy chief crown prosecutor for the CPS London, said: "Lawyers for the complainant have written to the CPS and asked us to review our decision.
"I have considered the matter personally and directed that all of the evidence should be reconsidered and a fresh decision taken by a senior lawyer with no previous involvement in this matter.
"That process will be completed as soon as possible and is the procedure we often adopt when pre-action protocol judicial review proceedings are initiated."
The Guardian reported that Mr MacFarlane also said to the man, who has not been named: "You'll always have black skin colour.
"Don't hide behind your colour, yeah," adding: "Be proud. Be proud of who you are, yeah. Don't hide behind your black skin."
Shortly before the recording ends, the man can be heard saying: "I get this all the time," and telling the officer: "Make sure you do a lot with your sixty grand, 'cos you're not going to get it no more, bruv."
He then tells the officer: "We'll definitely speak again about this. It's gonna go all the way, it's gonna go all the way - remember."
A Scotland Yard spokesman said: "We can confirm that the Metropolitan Police Service received a complaint alleging a man arrested on August 11 2011 was subjected to discriminatory behaviour (racial remarks); assault and oppressive conduct/or harassment.
"These are serious allegations; any use of racist language or excessive use of force is not acceptable.
"The MPS's Directorate of Professional Standards referred this case to the IPCC who are independently investigating.
"Following the alleged incident, three officers were the subject of a misconduct investigation. One of the officers has been suspended in relation to this matter pending the result of the IPCC investigation.
"One of the officers has been placed on restricted duties on an unrelated matter and another remains on full duties."