The Conservatives have called for the government to overrule planned changes which would make the ethnicity or faith of an offender a bigger factor when deciding whether to jail them.

The Sentencing Council, which issued the new guidance for England and Wales, is independent and ministers do not currently have the power to override it.

But shadow justice secretary Robert Jenrick told the BBC that if necessary, the law should be changed so the government could do so.

Justice Secretary Shabana Mahmood has said she will write to the council to “register my displeasure” and recommend reversing the change, after the Tories accused her of overseeing “two-tier justice”.

“As someone who is from an ethnic minority background myself, I do not stand for any differential treatment before the law, for anyone of any kind,” Mahmood said.

“There will never be a two-tier sentencing approach under my watch.”

The Sentencing Council said the updated guidance would ensure courts had the “most comprehensive information available” to hand out an appropriate sentence and could address disadvantages faced within the criminal justice system.

Official figures show that offenders from ethnic minorities consistently get longer sentences than white offenders for indictable offences.

If the Sentencing Council defies Mahmood, as they are entirely entitled to do, then the justice secretary and the prime minister face an acute dilemma.

Either they rush through legislation to overrule the council, no doubt facing down outrage from the legal establishment and anti-discrimination campaigners to do so.

Or they allow the guidelines to take effect, facing accusations from the Conservatives that they are not willing to do everything possible to stop something they themselves have described as “two-tier”.

That “two-tier” phrase is especially highly-charged. The government regards that accusation as politically toxic and is desperate to repel any suggestion of two-tier justice.

The updated sentencing guidance, which is due to come into force from April, places a greater emphasis on the need for pre-sentence reports for judges.

Pre-sentence reports give judges details on the offender’s background, motives and personal life before sentencing – then recommend a punishment and what would work best for rehabilitation.

But over recent years their use has decreased.

Magistrates and judges will be advised to get a pre-sentence report before handing out punishment for someone of an ethnic or faith minority – alongside other groups such as young adults, abuse survivors and pregnant women.

These factors are not an exhaustive list, the council said. A pre-sentence report can still be necessary if an individual does not fall into one of these cohorts.

However, Jenrick said this was a “blanket approach” that in many cases could lead to lesser sentences for certain groups.

He argued this could undermine the principle of equality of treatment under the law.

The shadow justice secretary told BBC Radio 4’s Today programme Mahmood had a representative at a meeting signing off the changes, who did not raise any objections.

The previous Conservative government was also consulted on the sentencing changes when the council was considering reforms between November 2023 and February 2024.

Pressed over why the Conservatives did not challenge the planned changes when they were in power, Jenrick said “there was no direction or requirement by government” for the council to investigate the issue.

He added that draft guidance had adopted less of a blanket approach, only saying a judge may produce a pre-sentencing report, rather than requiring them to do so.

However, he said the justice secretary at the time, Alex Chalk, had branded the idea “ridiculous and patronising”.

On Wednesday, Jenrick claimed the new guidelines were biased “against straight white men”.

“Under Two-Tier Keir [Starmer] our justice system is set to have an anti-white and anti-Christian bias,” he wrote on social media.

Sentencing Council chairman Lord Justice William Davis said the updated guidelines took into account “evidence of disparities in sentencing outcomes, disadvantages faced within the criminal justice system and complexities in circumstances of individual offenders”.

He added: “Pre-sentence reports provide the court with information about the offender; they are not an indication of sentence.”

The Prison Reform Trust said there were “very good reasons” for changes to sentencing guidelines.

Mark Daly, the charity’s deputy director, told Radio 4’s The World Tonight: “It has always been a factor that has been on the mind of sentencers and in this guideline it is simply reflecting the fact that if we look at outcomes from sentencing, there is disproportionality.

“So we know already that if you are from a minority ethnic background you are more likely to receive a custodial sentence for an equivalent offence, particularly for certain types of offences such as drug offences, than you would if you were white.”

He added: “It seems to me that this current dispute is a bit of a storm in a tea cup.”

Meanwhile, the guidance also advises courts should avoid sending pregnant women, or those who have given birth in the last 12 months, to prison.

The move was welcomed by campaigners, who said it finally recognised the “deadly impact” of prison on babies and pregnant women.