51.— (1) If, in any proceedings, an adoption order is declared invalid by a court and the child concerned is in the custody of—

(a) the person or persons in whose favour the adoption order was made, or

(b) any other person or persons not being the person or persons who sought the declaration of invalidity,

the court shall not make an order in those proceedings as to the custody of the child except in accordance with subsection (2).

(2) The court may make the order referred to in subsection (1), as to the custody of the child, if—

(a) the order is sought in the proceedings referred to in subsection (1), and

(b) the court is satisfied that, by reason of—

(i) the fact that any person having custody of the child has been joined in the proceedings, and

(ii) the other circumstances of the case,

it is in the interests of justice that the question of the custody of the child should be determined in those proceedings rather than in separate proceedings.

(3) However, if the court decides, in accordance with subsection (2), to determine the question of the custody of the child, the court shall do so subject to section 3 of the Guardianship of Infants Act 1964.

(4) Notwithstanding subsection (1)—

(a) the person or persons in whose favour an adoption order is made, or

(b) any other person or persons having custody of the adopted child,

shall not, without the consent of the court, be joined or otherwise heard in any proceedings in a court in which the validity of the order is an issue.

(5) In deciding whether to give consent under subsection (4), the court may take into account submissions made to it by the Authority or by any other interested person relating to—

(a) the identification, at the time of the submissions, of the person or persons concerned, or

(b) any other relevant matter.