Any person who has been convicted of a violation of subsection (b) of section 53-278b, subsection (d) of section 53-278c, subsection (a) of section 53-278d, or subsection (d) of section 53-278e or any statute predecessor thereto may, upon any subsequent violation of said subsections, be prosecuted as a persistent offender and on conviction may be subjected to the penalty of the next most serious classification of offense, provided it shall be an affirmative defense to the charge of being a persistent offender under this section if the defendant was pardoned on the ground of innocence with respect to the prior conviction on which the state is relying.