The consent of an untested former offender 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 former offender, and
(c) the signature is witnessed by a person other than a police officer, and
(d) the former offender is given a copy of the consent as soon as practicable after it is signed and witnessed.