Confession otherwise relevant not to become irrelevant because of promise of secrecy, etc.
29.  If such a confession is otherwise relevant, it does not become irrelevant merely because —
(a)it was made under a promise of secrecy, or in consequence of a deception practised on the accused person for the purpose of obtaining it, or when he was drunk;
(b)it was made in answer to questions which he need not have answered, whatever may have been the form of those questions; or
(c)he was not warned that he was not bound to make the confession and that evidence of it might be given against him.