• Minorities more likely to be jailed for certain crimes • Differences remain the subject of contention

Offenders from ethnic minorities are more likely than their white counterparts to be sentenced to prison for certain categories of crimes, according to an analysis of more than one million court records.

The study, carried out by the Guardian, found black offenders were 44% more likely than white offenders to be sentenced to prison for driving offences, 38% more likely to be imprisoned for public disorder or possession of a weapon and 27% more likely for drugs possession.

Asian offenders were 41% more likely to be sent to prison for drugs offences than their white counterparts and 19% more likely to go to jail for shoplifting.

The findings, which accord with a history of academic research into disparities, suggest wider variations in sentencing than in some previous studies and also show variation between courts.

Frances Done, chair of the Youth Justice Board, who is working with the Magistrates' Association on disparities in sentencing, told the Guardian that she fears the "disproportionality appears to be getting worse".

She added: "As the numbers in [youth] custody have gone down, the proportion of those from black and ethnic backgrounds has gone up. We don't get the view that this is about deliberate discrimination but because of practices that have not been thought through."

One cultural difference, Done said, is a "greater propensity for black young people not to plead guilty than white young people". Black youths consequently received longer sentences because credit is given for early guilty pleas.

Differences in sentencing between ethnic groups have been a subject of academic contention for a while. Some explanations suggest offenders from different ethnic minorities commit more serious offences in particular categories or have longer criminal histories; others speculate they could be indicative of prejudice in areas of the criminal justice system.

The Ministry of Justice this week released details of all 1.2 million sentences passed by English and Welsh courts between July 2010 and June 2011, including information on the age and ethnicity of defendants, if available.

The Guardian used that information on offences where ethnicity information was available – a huge sample of more then 596,000 individual judgments – to compare the outcomes for different ethnic groups.

The smallest variance found was in shoplifting, where black defendents were just 1.7% more likely than white to be imprisoned, while the largest was driving offences, for which black defendents were jailed 44.3% more frequently than white.

The Judicial Office said it was worth noting that last year's Race and CJS report found data on out-of-court disposals and court proceedings showed differences in the sanctions issued to people of differing ethnicity and also in sentence lengths. These differences possibly related to a range of factors including types of offences committed and the plea entered, and should be treated with caution.

The difference in racial sentencing between courts was also considerable. Haringey magistrates court, which dealt with many of the Tottenham riot cases, sentenced – before the summer disturbances – 11 of the 54 black defendants it dealt with for public disorder or weapons offences to prison, as compared to 5 of 73 white defendants.

While West London magistrates court sentenced 17 of 107 black defendents to jail, versus 21 of 237 who were white – meaning at that court black defendents were 79% more likely to be jailed. By contrast, at Wolverhampton Crown Court, which dealt with a similar number of public disorder cases, the difference was just 4%.

A previous study investigating the sibility of discrimination in patterns of sentencing was carried out by Roger Hood in the West Midlands in 1992. It also found variations across courts, with one recording that black male defendants had a 23% greater probablity of a custodial sentence than a white male.

The government's official statistics on "Race and the Criminal Justice System", published by the Ministry of Justice last month, reveal that for all indictable offences in 2010, black offenders are 17% more likely to receive immediate custodial offences than white offenders.

– but a breakdown for offences was not available.

John Fassenfelt, chairman of the Magistrates' Association, said that JPs had been trying to get behind the disparityto see whether it is due to magistrates sentencing black people harder or whether there's more criminality [in certain communites]."

In some inner city areas with large black communities, he said, there might not be sufficient diversity on magistrates' benches.

Professor Mike Hough, of the Institute for Criminal Policy Research, Birkbeck College, said the latest statistics showed a possibility of discriminatory sentencing practices but the statistics on their own did not prove it.

He extracted the figures for those sentenced for indictable offences. The percentage of those given immediate custody was 24% for white defendants, 27% for black defendants and 29% for Asian defendants.

"They are a worrying set of statistics," he said. "At face value they suggest that defendants from minority groups face a somewhat higher risk of going to prison than similar white defendants. In some areas the difference in risk may be quite large.

"For youth justice, the picture is that over-representation of minority groups as they enter into the criminal justice system is largely preserved (rather than amplified or reduced) as young people pass through. But black defendants were more likely to be remanded in custody, and more likely to end up sentenced to custody".

Many explanations have been advanced for the disparity, he said, including the possibility of different patterns of charging by police or the crown prosecution service, different patterns in remand decisions, 'over-policing' of ethnic groups or social deprivation.

Others suggest that ethnic groups are concentrated in inner cities where they are more likely to come up before district judges, formerly stipendiary magistrates, who may sentence more heavily.

Dr Coretta Phillips, at the London School of Economics' Mannheim Centre for the Study of Criminology and Criminal Justice, said: "The raw figures [in the MoJ] data are unable to take account of all the relevant legal factors which might explain these patterns.

"The research evidence on the sentencing of young offenders is complex, but there is some indication that racial discrimination plays a part in conviction, remand, and possibly sentencing patterns, in some areas, some of the time.

"[But] on the basis of the data published yesterday, it would be hard to conclude anything about prejudice and discrimination from the magistracy or judiciary or that there is greater criminality among minority groups."

The Ministry of Justice said: "Sentencing is entirely a matter for the courts, where decisions are taken by independent magistrates and judges based on the individual circumstances of each case. There are many factors behind sentencing decisions, including the seriousness of each offence and the impact of guilty pleas which lead to reduced sentences."