The implications in such circumstances are detailed in a written answer on 31 March 1993 by the then Attorney General (Sir Nicholas Lyell), as outlined below.
The fundamental consideration remains that individuals should be able to rely on decisions taken by the prosecuting authorities. The policy of the Director of Public Prosecutions is that a decision to terminate proceedings or not to prosecute should not, in the absence of special circumstances, be altered once it has been communicated to the defendant or prospective defendant unless it was taken and expressed to be taken because the evidence was insufficient. In such a case it would be appropriate to reconsider the decision if further significant evidence were to become available at a later date especially if the alleged offence is a serious one.
Special circumstances which might justify departure from this policy include:
(1) rare cases where reconsiderations of the original decision show that it was not justified and the maintenance of confidence in the criminal justice system requires that a prosecution be brought notwithstanding the earlier decision; and
(2) those cases where termination has been effected specifically with a view to the collection and preparation of the necessary evidence which is thought likely to become available in the fairly near future. In such circumstances the CPS will advise the defendant of the possibility that proceedings will be re-instituted. (Official Report, Col’s 200-201).
Following this written answer and further written ministerial statements, the Crown Prosecution Service has produced guidance for prosecutors to follow concerning the exercise of the CPS discretion to institute, reinstitute or continue proceedings after a suspect has been informed by the police or CPS of a decision not to prosecute. The above mentioned Written Statements are detailed below and are published in the Official Report.
WMS – Crown Prosecutors Code - 22 February 2010. Column WS64, Baroness Scotland of Asthal.
WMS - Reconsidering a Prosecution Decision (CPS Guidance) - 31 October 2012, Col 15WS, Rt. Hon Dominic Grieve
WMS – Victim’s Right to Review - 5 June 2013, Col 99WS, Rt. Hon Dominic Grieve