The theoretical basis for the common law power of alteration was that no sentence was finally and conclusively decided until it was made a matter of record by either the (court of assizes) judge's or the (quarter sessions) clerk of the peace's signing. Once the document detailing all sentences imposed during that assize or quarter session was signed, only an appeal court could make an alteration. When the courts of assizes and quarter sessions were replaced by the Crown Court, the power of alteration was given statutory basis and specified periods (28 days) and provisions governing alterations were established. The statutory jurisdiction of Crown Court judges to alter sentences and other orders is equivalent to that granted by common law, though the words used in two critical sections of the law probably result in a lack of power to alter orders made in respect to persons who have not been convicted. There is, however, jurisdiction to increase sentences, to add to sentences, to change the nature of sentences, and to vary sentences due to developments since the data on which the original sentence was imposed. The court of appeal can, as in the three landmark cases, Menocal, Grice and Sodhi, assert a right to reject alterations which are inappropriate in regard to the sentence originally imposed and to all other circumstances of the case. It is suggested that the court of appeal should be prepared to review the trial judge's exercise of the discretion to alter. In an extreme example, a trial judge should not be allowed to alter a sentence from probatiom to imprisonment merely because the judge felt, after a few days' reflection, that the probation sentence was too lenient. Case notes are appended. (Author abstract modified)