Taken from the updated act.
1 (1) For the purposes of this Schedule a caution shall be regarded as a spent caution�
(a) in the case of a conditional caution (as defined in section 8A(2)(a)), at the end of the relevant period for the caution;
(b) in any other case, at the time the caution is given.
(2) In sub-paragraph (1)(a) �the relevant period for the caution� means (subject to sub-paragraph (3)) the period of three months from the date on which the conditional caution was given.
(3) If the person concerned is subsequently prosecuted and convicted of the offence in respect of which a conditional caution was given�
(a) the relevant period for the caution shall end at the same time as the rehabilitation period for the offence; and
(b) if the conviction occurs after the end of the period mentioned in sub-paragraph (1)(a), the caution shall be treated for the purposes of this Schedule as not having become spent in relation to any period before the end of the rehabilitation period for the offence.
And then once it becomes spent
3 (1) A person who is given a caution for an offence shall, from the time the caution is spent, be treated for all purposes in law as a person who has not committed, been charged with or prosecuted for, or been given a caution for the offence; and notwithstanding the provisions of any other enactment or rule of law to the contrary�
(a) no evidence shall be admissible in any proceedings before a judicial authority exercising its jurisdiction or functions in England and Wales to prove that any such person has committed, been charged with or prosecuted for, or been given a caution for the offence; and
(b) a person shall not, in any such proceedings, be asked and, if asked, shall not be required to answer, any question relating to his past which cannot be answered without acknowledging or referring to a spent caution or any ancillary