Home Secretary Yvette Cooper told reporters that “greater transparency” would be a “step forward”.
The Home Office oversees police in England and Wales. The guidance was developed by the National Police Chiefs’ Council and the College of Policing.
“Disinformation and incorrect narratives can take hold in a vacuum,” said council spokeswoman Sam de Reya, deputy chief constable for Hampshire and the Isle of Wight.
“It is good police work for us to fill this vacuum with the facts about issues of wider public interest.”
False claims that the suspect accused of killing girls aged 6, 7, and 9 at a dance class in Southport last July was a Muslim asylum-seeker fuelled days of unrest in England and Northern Ireland.
Rioters surrounded mosques, burned businesses and vehicles, and attacked people. More than 130 police officers were assaulted, authorities say, and more than 1800 people arrested.
The 17-year-old who later pleaded guilty to the killings was a Christian and British citizen born in Wales and raised in England.
When two men were charged last month in the rape of a 12-year-old girl near Birmingham, the anti-immigration Reform UK party alleged that they were Afghan asylum-seekers.
When police declined to release the suspects’ ethnicities or nationalities, the party accused them of a cover-up.
The case drew fresh criticism for Prime Minister Keir Starmer’s Labour Government, now trailing Nigel Farage’s Reform UK in polling. Cooper suggested then that the guidelines would be updated.
Advocates for migrants warned that the guidance would not address broader anti-migrant sentiments in Britain.
“Releasing the ethnicity and nationality of suspects is simply a concession to far-right anti-migrant dogwhistles,” said Julia Tinsley-Kent, head of policy at the London-based Migrants’ Rights Network.
“All this does is signal that it is somehow legitimate to riot in scenarios where the suspect is a racialised person.”
Shabna Begum, chief executive of the pro-gender-equality, anti-racist Runnymede Trust, said it could also implicitly frame crimes against women and girls as issues of ethnicity.
“The motivation for this narrative cannot claim to have women’s safety as its primary concern,” she said.
“There is no evidence to suggest women will be any safer by making sexual violence appear to have a racialised nature.”
“These are cheap political tricks that address none of the urgent problems but cause deep, long-lasting harm.”
In May, police took the unusual step of identifying the man accused of driving a minivan into a crowd of soccer fans in Liverpool as a white British citizen.