90.— (1) A person who, by reason of section 89 , is subject to the requirements of this Part shall be so subject for the period referred to in subsection (3) or, in the case of a person referred to in subsection (2) or (3) of section 89 , so much (if any) of that period as falls after the commencement of this Part.

(2) Subsection (1) is subject to section 93 .

(3) The period mentioned in subsection (1) is the period, beginning with the relevant date, of—

(a) 12 years if the sentence imposed on the person in respect of the offence concerned is one of imprisonment for life,

(b) 7 years if the sentence imposed on the person in respect of the offence concerned is one of imprisonment for a term of more than 10 years but not one of imprisonment for life,

(c) 5 years if the sentence imposed on the person in respect of the offence concerned is one of imprisonment for a term of more than 5 years but not more than 10 years,

(d) 3 years if the sentence imposed on the person in respect of the offence concerned is one of imprisonment for a term of more than one year but not more than 5 years,

(e) one year if the sentence imposed on the person in respect of the offence concerned is one of imprisonment for any term, the operation of the whole of which is suspended (but, if the operation of that term is revived by the court, whichever of the preceding paragraphs is appropriate shall apply instead of this paragraph).

(4) If—

(a) a sentence is imposed on a person in respect of a drug trafficking offence, and

(b) at the time of sentencing the person is aged under 18 years,

subsection (3) shall have effect in relation to that person as if for the references to 12 years, 7 years, 5 years, 3 years and one year in that subsection there were substituted references to 6 years, 3½ years, 2½ years, 1½ years and 6 months, respectively.

(5) If a sentence of imprisonment for any term is imposed on the person referred to in subsection (1) in respect of the offence concerned and the operation of a part of that term is suspended—

(a) the part of that term the operation of which is not suspended shall be regarded as the term of imprisonment imposed on that person for the purposes of subsection (3) (but, if the operation of the first-mentioned part of that term is revived by the court, whichever of paragraphs (a) , (b) , (c) and (d) of subsection (3) is appropriate shall apply without regard to this paragraph),

(b) paragraph (a) extends to a case in which that suspension is provided for subsequent to the imposition of the sentence.

(6) If a person is or has been sentenced in respect of 2 or more drug trafficking offences and the sentences imposed are consecutive or partly concurrent then subsection (3) shall have effect as if—

(a) in the case of consecutive sentences, the sentence imposed in respect of each of the offences were or had been a sentence equal to the aggregate of those sentences,

(b) in the case of partly concurrent sentences, the sentence imposed in respect of each of the offences were or had been a sentence equal to the aggregate of those sentences after making such deduction as is necessary to ensure that no period of time is counted more than once.

(7) Without prejudice to section 93 , a person shall cease to be subject to the requirements of this Part if the conviction in respect of the offence concerned is quashed on appeal or otherwise.

(8) A reference in this section to a sentence imposed on a person shall, if the sentence is varied on appeal, be construed as a reference to the sentence as so varied and, accordingly, the period for which a person is subject to the requirements of this Part, by reason of this section, shall stand reduced or increased, as the case may be, in the event that such a variation is made which results in the sentence falling under a different paragraph of subsection (3) than it did before the variation.