(1) The credibility rule does not apply to evidence given by a person concerning the credibility of another witness if—
(a) the person has specialised knowledge based on the person's training, study or experience; and
(b) the evidence is evidence of an opinion of the person that—
(i) is wholly or substantially based on that knowledge; and
(ii) could substantially affect the assessment of the credibility of the witness; and
(c) the court gives leave to adduce the evidence.
(2) To avoid doubt, and without limiting subsection (1)—
(a) a reference in that subsection to specialised knowledge includes a reference to specialised knowledge of child development and child behaviour (including specialised knowledge of the impact of sexual abuse on children and their behaviour during and following the abuse); and
(b) a reference in that subsection to an opinion of a person includes, if the person has specialised knowledge of that kind, a reference to an opinion relating to either or both of the following—
(i) the development and behaviour of children generally;
(ii) the development and behaviour of children who have been victims of sexual offences, or offences similar to sexual offences.