17.—(1) A person, other than a person to whom section 16 applies, shall be guilty of an offence who, without lawful authority or reasonable excuse, intentionally takes or detains a child under the age of 16 years or causes a child under that age to be so taken or detained—

( a ) so as to remove the child from the lawful control of any person having lawful control of the child; or

( b ) so as to keep him or her out of the lawful control of any person entitled to lawful control of the child.

(2) It shall be a defence to a charge under this section that the defendant believed that the child had attained the age of 16 years.

(3) A person guilty of an offence under this section shall be liable—

( a ) on summary conviction to a fine not exceeding £1,500 or to imprisonment for a term not exceeding 12 months or to both, or

( b ) on conviction on indictment to a fine or to imprisonment for a term not exceeding 7 years or to both.