Prosecuting counsel may be put under a new duty to provide judges with a written memo setting out their sentencing powers after a spate of criminal cases in which judges passed unlawful sentences.

The lord chief justice, Lord Phillips, has asked the criminal procedure rules committee to consider imposing the requirement after the appeal court quashed the sentences passed on four men convicted of a range of offences including child rape, burglary and carrying an offensive weapon. In all four cases, the judges had passed sentences which went beyond their powers.

Judges complain that the volume of sentencing law changes has made the job of passing sentence difficult. The four judges who imposed the wrong sentences were not criticised by the lord chief justice, who reserved his criticism for the advocates in the cases.

Delivering the appeal court's judgment in the four cases last month, Lord Phillips commented: "It is of course the duty of a judge to impose a lawful sentence, but sentencing has become a complex matter and a judge will often not see the papers very long before the hearing and does not have the time for preparation that advocates should enjoy. In these circumstances a judge relies on the advocates to assist him with sentencing."

He said it was "unacceptable" for defence advocates "not to ascertain and be prepared to assist the judge with the legal restrictions on the sentence that he can impose on their clients". There was also a duty on the prosecuting advocate "to ensure that the judge does not, through inadvertence, impose a sentence that is outside his powers."

Lawyers had been urged to adhere to these duties in earlier appeal court judgments in 2003 and 2005 after trial judges had passed unlawful sentences. "What causes us particular concern is that, as the appeals before us demonstrate, there appears to be a widespread disregard of these judicial admonitions."

Lord Phillips said the only way of achieving what was needed might be for the prosecuting advocate to be required to draw up a memo for the judge. He invited the rules committee to consider making this a requirement.

In some of the cases the advocate had not even picked up the fact that the sentences were unlawful when preparing the appeal, and the appeal was based on other grounds. It was the appeal court staff who had noticed that the sentences went beyond the judges' powers.

In all four cases the three senior judges headed by Lord Phillips passed lawful sentences in place of the unlawful ones, reducing the sentences in three of the four cases.

In the fourth, a case of child rape, buggery and indecency with children, the substituted sentences added up to the same 13-year sentence of imprisonment as the trial judge had imposed.