The following subsection shall be substituted for subsection (1) of section fifty-seven of the Children and Young Persons (Scotland) Act, 1937:—
“(1)Sentence of death shall not be pronounced on or recorded against a person convicted of an offence if it appears to the court that at the time when the offence was committed he was under the age of eighteen years; but in lieu thereof the court shall sentence him to be detained during His Majesty's pleasure; and if so sentenced he shall be liable to be detained in such place and under such conditions as the Secretary of State may direct.”