More lawyers are to be recruited to a scheme that reviews “unduly lenient” sentences after a sharp rise in the number of complaints about judges’ decisions on jail terms.



The attorney general, Jeremy Wright QC, is to announce on Wednesday an extension of the legal programme that allows prosecutors to review cases on behalf of the government. The number of sentences considered by his office under the unduly lenient sentence (ULS) scheme soared by 97% between 2010 and 2014, from 342 cases to 674.

For a sentence to be reviewed, the attorney general’s office must receive a complaint from at least one member of the public. Not every submission results in a referral, but between 2010 and 2014 the number of cases the attorney general’s office sent to the court of appeal rose by 35%, from 90 to 122.



Complaints can only be made about crown court sentences imposed for particular types of crime, including murder, rape, robbery, child sex crimes, fraud, drug offences and those committed because of the victim’s race or religion. They must be lodged within 28 days of sentencing.



Legal reviews are currently conducted by a small number of highly qualified barristers, known as treasury counsel. But other senior lawyers – those classed as grade four prosecution advocates by the Crown Prosecution Service – will now be recruited to the ULS scheme for a six-month pilot period.



At last year’s general election, the Conservative party manifesto included a pledge to widen the scope of powers to refer sentences, in order to include less serious offences.



The attorney general said: “It’s vital that the public are able to legally challenge custodial sentences and to make sure offences are being properly punished.



“This trial extension is a great opportunity for experienced lawyers to develop their skills further while preserving the continued effective operation of the ULS scheme. With the number of referrals increasing, it is right that we look at ways to widen the approach.”



Wright and the solicitor general, Robert Buckland QC, appear in many of the court of appeal sentencing cases. In some cases, prison terms are significantly extended.



In one recent case, a sentence for rape was increased from five and a half years to 12 years in prison. In 2014, it has been calculated, more than 100 years of additional jail time was added to sentences reviewed under the ULS scheme. The prison population in England and Wales is currently more than 85,000.



Responding to statistics on ULS cases, the president of the Queen’s bench division, Sir Brian Leveson, said: “The number of sentences found to be unduly lenient following consideration by the attorney general or solicitor general continues to be low.



“In 2013 and 2014, only 166 offenders had their sentence increased, a very small fraction of the many thousands of offenders sentenced for relevant offences in the crown court that year.



“Sentencing is a complex process where the judge must take into account a number of factors in reaching a balanced decision. In order to maintain public confidence in sentencing, it is important that any member of the public may request a review by the attorney general of a sentence imposed in the crown court.”