Prime Minister Sir Keir Starmer says there are "serious questions for police" following the release of bodycam vision showing how officers responded to the murder of teenager Henry Nowak.
His killer Vickrum Digwa, 23, was jailed on Monday for life to serve a minimum of 21 years for stabbing Nowak with a 21cm (8in) blade he said he carried as part of his Sikh faith.
Bodycam footage shows the 18-year-old Southampton university student being handcuffed and telling police "I can't breathe" after Digwa lied to officers at the scene of the stabbing, claiming he was the victim of a racist attack.
Sir Keir said the question of "how accusations of racism informed decision making" must be addressed.
Speaking to broadcasters, he said the bodycam footage was "really harrowing" and he'd "felt sick watching it".
The Independent Office for Police Conduct (IOPC) said an investigation into the police force's actions was ongoing.
Sir Keir said he wouldn't rule out an inquiry into the matter, saying "it's important the IOPC do their work at first, but I'm not saying there shouldn't be a wider inquiry. Of course I'm not".
Warning: This story contains details some may find upsetting
Earlier, Home Secretary Shabana Mahmood called out a "dangerous undercurrent" in reaction to crimes, which she says are leading to threats.
A police officer has been "forced to relocate to protect himself and his family", after being wrongly identified online as being involved in the case, she said.
In an address to the House of Commons, Mahmood warned against opposition MPs politicising the case.
Reform UK leader Nigel Farage told reporters he had a sense of "cold rage" at the treatment of Nowak and labelling it evidence of a "two-tier Britain".
"A false accusation of racism counted higher at that moment than someone that was dying," he said.
In a statement to the House of Commons, shadow home secretary Chris Philp said the "police appeared more concerned with the accusation of racism… than they were with helping Henry".
Mahmood said that while it was for the IOPC to determine the facts of the specific case, she responded to allegations of preferential treatment by police more broadly.
"The police in this country have a sacred duty to police without fear or favour. Everyone in this country is equal before the law," she said.
The prime minister's official spokesman said there is "no such thing as two-tier policing".
Labour MP Tanmanjeet Singh Dhesi, himself a Sikh, accused Reform UK and other far-right parties of deciding to "scapegoat" the Sikh community "based on the actions of one violent murderer."
The attorney general's office is considering the jail sentence given to Vickrum Digwa after receiving "multiple requests" to review it under the unduly lenient sentence (ULS) scheme.
Under current legislation, practising Sikh's have a legal defence for wearing a small, curved blade, known as a kirpan, close to their body for religious purposes.
While Digwa had been wearing a traditional kirpan under his clothing, the weapon he used on Nowak was much bigger and he had worn it in a sheath on top of his clothes.
Digwa's family apologised to Nowak's family and for bringing the Sikh community into "disrepute".
"We love Vickrum. We will continue to love him. That love does not stand in opposition to the sorrow we feel for the Nowak family. Both are real, and both will remain with us for the rest of our lives," an unnamed family member said in a statement.
In her address, Mahmood said she "echoed" the comments of the prosecutor in the case, who said: "This is not a case about Sikhism, this is not a case about racism, this is a case about murder."
That quote was also cited by Nowak's family, who called his treatment by police "inhumane and degrading" and the force has apologised.
His dad, Mark, said: "Henry told officers that he could not breathe nine times. He told them that he had been stabbed four times. Henry was pulled across the gravel, his hands forced behind his back and he was placed in handcuffs."
He said the contrast between how his son and Digwa had been treated was "unbearable".
"Henry should not have died on the streets of Southampton in police custody," he added.
Three of the officers involved are still serving, and one has resigned, a spokesperson for the Hampshire & Isle of Wight Constabulary said.
Donna Jones, the Police and Crime Commissioner for Hampshire and the Isle of Wight, has separately requested a review of the culture and performance of the police force's control room and the training of officers responding to the stabbing.
In the bodycam footage a police officer arriving at the scene can be heard asking: "What's your name, mate?" before Nowak, who is lying on his back on the ground, faintly replies: "Henry."
As the video continues, Digwa steps into the frame claiming Nowak had taken his turban off and grabbed him by the hair.
The officer asks Digwa: "Are you injured?" to which Digwa replies: "Yeah, yeah, I've got a swollen eye here, a little bruise here."
Officers then turn to Nowak who can be heard repeating "I've been stabbed" and then "I can't breathe" while he is made to sit up to be handcuffed.
As the footage continues, the officer can be heard asking: "You've been stabbed, whereabouts?" before adding: "Don't think you have, mate."
While being handcuffed, Nowak says "I can't breathe" another three times.
The officer can be heard saying: "He says he's been stabbed, so let's just check him" and appears to briefly lift his shirt around the belt area before Nowak is left to lie on his side.
A female officer can then be heard asking: "Where do you think he's been stabbed? In the face?" to which a male voice replies: "He hasn't been stabbed."
Nowak, who seems unresponsive, is then told he is being arrested for assault.
In his sentencing remarks, Judge William Mousley KC said that no matter how quickly Nowak received "first aid, CPR or expert medical treatment", he would not have survived due to the nature of his injuries.
On Tuesday evening, about 250 to 300 people gathered outside Southampton Police station, including far-right figure Tommy Robinson.
Some held signs and waved union jack flags while a line of officers blocked steps leading to the station.
Separately, Digwa's father Moga Singh, 52, and brother Gurpreet, 27, faced court on Tuesday afternoon.
They each face multiple charges for possession of an offensive weapon in a private place, among the weapons were an extendable baton, knuckle dusters, flick knife, sword and machete.
Gurpreet Digwa faces separate charges for having an offensive weapon in public, including an axe and possession of a prohibited weapon which was an air rifle.
Moga Singh and Gurpreet Digwa were released on unconditional bail.
His mother Kiran Kaur, 53, was found guilty of assisting an offender after she attempted to hide the blade used in the attack. She will be sentenced on 17 July.
Additional reporting by Curtis Lancaster and Peter Cooke
