Sir Paul Stephenson has ordered a review of uniforms worn at protests
Officers who deliberately conceal their identification numbers will face the sack, Britain's top policeman has said.
Metropolitan Police Commissioner Sir Paul Stephenson said it was "totally unacceptable" not to wear the numerals.
His comments follow allegation against several officers at the G20 protests - including the man who pushed newspaper seller Ian Tomlinson before he died.
New footage has emerged of the moments leading up to his death, as a third post-mortem examination was held.
Mr Tomlinson, 47, died minutes after he was pushed over during the demonstrations in central London.
The officer at the centre of the allegations has been suspended and interviewed under caution on suspicion of manslaughter.
Two previous post-mortem examinations have come to different conclusions on the cause of death - one coronary artery disease, the other abdominal bleeding.
Sir Paul said: "If somebody is trying to deliberately avoid being identified and the reason he is doing it is so he can behave inappropriately, badly or criminally, then of course they will face the sack."
He added that proper identification was not just a check on their behaviour but a way of protecting them against false allegations.
But he told reporters at Scotland Yard there were concerns about how identification badges were attached to specialist uniforms.
When he visited Tamil supporters protesting in London earlier this week, a sergeant's epaulettes had slipped down his arm, Sir Paul said.
A Territorial Support Group officer filmed without identification during the Tamil protests has since been disciplined.
Sir Paul has ordered a review of uniforms worn during demonstrations and said he would deal "appropriately but proportionately" with any breaches.
Meanwhile, new footage has emerged showing the moments leading up to the death of Mr Tomlinson.
The Independent Police Complaints Commission (IPCC) had tried to secure a court order preventing Channel 4 News showing the film, but a judge refused to grant the injunction.
The IPCC said the film - which will be broadcast on Wednesday - could have damaged its investigation, but ITN argued it was a "responsible piece of journalism".
IPCC chairman Nick Hardwick, who is leading an inquiry into the G20 protests, has been accused by the Police Federation of conducting a witchhunt.
Members are angry that Mr Hardwick gave media interviews in which he expressed criticism of officers' behaviour.