Keir Starmer has condemned rioting in Southampton on Tuesday night, saying it was “a time for serious work, not rage” in a direct attack on Nigel Farage’s response to the murder of Henry Nowak.

Speaking at prime minister’s questions, Starmer responded to a question by the Reform UK leader about supposed “two-tier policing”, calling Farage’s actions “unforgivable”.

In his opening remarks, Starmer said Nowak’s family had “shown extraordinary dignity after their son’s life was stolen in appalling circumstances”.

He added: “There are serious questions to answer, including how accusations of racism informed police thinking,” saying the government would support the Independent Office for Police Conduct in its investigation of the case.

The police watchdog is examining the conduct of the officers who handcuffed Nowak, 18, after he had been fatally stabbed by Vickrum Digwa, 23. They had gone to the scene after Digwa falsely claimed he had been racially abused and attacked by Nowak.

Starmer said: “No matter the pain we feel, there is no justification for more violence and disorder. The attacks directed towards police officers in Southampton last night were disgraceful and completely unacceptable.

“This is a time for serious work, not rage. And let me be clear, we will ensure anyone found engaging in disorder meets the full force of the law, as we have done before.”

Eleven police officers and one police dog were injured after crowds including far right agitators attacked officers in Southampton in what was billed as a protest about Nowak’s death and his treatment by police.

In a social media statement on Tuesday, Farage called for the public to respond with “pure, cold rage”, saying bodycam footage of Nowak’s treatment showed that the rights of minority ethnic Britons were prioritised over those of white citizens.

In a statement after Digwa was jailed on Monday, Nowak’s father made a statement outside court urging people not to use the death to provoke division.

Referring to the statement, Starmer said: “I think those words have resonated with people across the country. We must not allow this tragedy to be hijacked by anyone who seeks to divide us.”

Farage said it was “clear to growing millions in this country that we’re living under two-tier policing”, saying this led to what he called “the anger that you saw spilling out in Southampton last night”.

In a response, Starmer called Farage’s comments “unforgivable”.

He said: “A grieving family have asked us not to respond in the way that the leader of Reform has responded. They’ve asked us not to. They have lost their son in the most appalling circumstance. They make a simple plea of us as human beings to please not exploit that. That is their plea to us.

“We all need to reflect on those words of Henry’s father. My response and the response of others to be fair has been focused on the lessons to be learned so we can deliver justice.

“His response has been to appeal for rage – rage. That’s his response to a father who has lost his son and asked for that not to happen. Exploiting this tragedy to create grievance and division would be wrong in any circumstances, but to do it when the family are expressly saying please don’t is unforgivable. It shows exactly who he is.”

Speaking earlier on Wednesday, the policing minister, Sarah Jones, condemned the violence, also saying that anti-discrimination guidance to police that black and white suspects should be treated differently “gives the wrong impression”.

The National Police Chiefs’ Council (NPCC) announced it would review the anti-racism guidance, which advises police to treat ethnic minorities differently to get them better outcomes, and which some have blamed for the actions of the officers who arrested Nowak.

Nick Timothy, the shadow justice secretary, said in an interview on BBC Breakfast on Wednesday: “Our law enforcement and our criminal justice system are being corrupted by political correctness and leftwing ideology.”

The NPCC says in its anti-racism commitment that it aims for “equality of policing outcomes of people from different ethnic groups by responding to individuals and communities according to their specific needs, circumstances and experiences”, and that this does not mean treating everyone the same or being colourblind.

Jones told BBC Radio 4’s Today programme: “We think the language is wrong and it gives the wrong impression. I don’t think it affects how our training is doing, but people are right to ask questions when they have seen such an horrific incident.”

On Times Radio, Jones said: “Everyone must be equal under the law and we must ensure that is the case,” adding: “We can’t shy away from what are historic and legitimate concerns about racism within police forces.”