Evidence of a prior statement, oral or written, made by a witness is not made inadmissible by the hearsay rule if the prior statement is inconsistent with his testimony at a hearing or trial. After the witness has been given an opportunity at such hearing or trial to explain or deny the prior statement, the court shall allow either party to prove that the witness has made a prior statement, oral or written, inconsistent with his sworn testimony. Such prior statement shall be admissible for the purpose of affecting the credibility of the witness or for proving the truth of the matter asserted therein if it would have been admissible if made by the witness at the hearing or trial. Each party shall be allowed to cross-examine the witness on the subject matter of his current testimony and the prior statement.