The consent of a volunteer, or a parent or guardian of a volunteer, to the carrying out of a forensic procedure under this Part is not effective unless--
(a) the consent is in writing and in a form containing the particulars prescribed by the regulations, and
(b) the consent is signed by the volunteer, parent or guardian, and
(c) the signature is witnessed by a person other than a police officer or other person involved in the investigation of an offence to which the forensic procedure relates, and
(d) the volunteer, parent or guardian is given a copy of the consent as soon as practicable after it is signed and witnessed.