A sentence of detention during the pleasure of the Governor-General of Jamaica, authorised by s.29(1) Juveniles Act 1951, was incompatible with the Constitution of Jamaica because it infringed the constitutional principle that judicial functions (such as sentencing) had to be exercised by the judiciary and not by the executive. A sentence of life imprisonment, with a recommendation as to the minimum term to be served, could not lawfully substituted for such a sentence. The only permissible sentence was detention during the court's pleasure.Appeal and cross-appeal from a decision of the Court of Appeal of Jamaica by which it allowed the defendant's ('M') appeal against a sentence of detention during the pleasure of the Governor-General and substituted a sentence of life imprisonment with a recommendation that M should not be considered for parole until he had served a period of 20 years' imprisonment. In 1994, when he was aged 16, M committed the offence of capital murder. Following his conviction, he was sentenced under s.29(1) Juveniles Act 1951 to be detained during the Governor-General's pleasure. M appealed against sentence, contending that s.29(1) was incompatible with the Constitution of Jamaica, which had been established in 1962. In particular, he contended that a sentence which authorised his detention at the discretion of the executive, in the form of the Governor-General, was incompatible with his constitutional right, under s.15 and s.20 of the Constitution, not to be deprived of his liberty otherwise than in the execution of the sentence or order of the court. The Court of Appeal allowed M's appeal and substituted the sentence set out above. The appellant ('the DPP') appealed against the finding of incompatibility, on the ground that s.26(8) of the Constitution expressly preserved any law which pre-dated the Constitution. M cross-appealed against the imposition of a sentence which he contended was more disadvantageous than the sentence originally imposed.HELD: (1) The Board accepted M's argument that the power to detain him at the discretion of the executive infringed the constitutional principle that judicial functions (such as sentencing) had to be exercised by the judiciary alone. (2) Although the Constitution expressly preserved any pre-existing law, it did not render those laws immune from challenge under the Constitution. (3) The Board had no doubt that the court had power to vary or modify s.29 of the 1951 Act so as to render it compatible with the Constitution. (4) In seeking to vary or amend the sentence of detention by imposing a fixed life term, the Court of Appeal had imposed a sentence more disadvantageous to M than that originally imposed. The only permissible sentence was detention during the court's pleasure.Judgment accordingly.
 UKPC 6