5Appeals where previous convictions set aside
(1)This section applies where—
(a)a sentence has been imposed on any person under subsection (2) of section 2, 3 or 4 above; and
(b)any previous conviction of his without which that section would not have applied has been subsequently set aside on appeal.
(2)Notwithstanding anything in section 18 of the [1968 c. 19.] Criminal Appeal Act 1968, notice of appeal against the sentence may be given at any time within 28 days from the date on which the previous conviction was set aside.