(1)Subject to the provisions of this section, where a person serving a sentence of detention in a young offenders institution has attained the age of 21 years, the Secretary of State shall have power to transfer him to prison.
(2)No person shall be detained in a young offenders institution after he has attained the age of 23 years, and accordingly any person so detained shall, not later than the day immediately preceding his twenty-third birthday, be transferred to prison.
(3)Where a person has been transferred to prison under this section, he shall be treated for the purpose of his serving the unexpired part of his sentence and of his supervision on release as if the sentence of detention passed upon him were a sentence of imprisonment for a like term, and the provisions of the 1975 Act and this Act relating to the treatment and supervision of prisoners shall apply to him accordingly:
Provided that section 212, or as the case may be section 421, of the 1975 Act (recall on reconviction) shall continue to apply to a person so transferred to prison.