Failing to Obtain, Losing or Destroying Evidence
The leading case is R (Ebrahim) v Feltham Magistrates’ Court  1 All ER 831. The starting point must be whether there was a duty on the investigator to obtain and/or retain the material in question. That question will be answered primarily through the provisions of the Code of Practice issued under Part II of the CPIA 1996.
If there was no duty to obtain or retain the evidence in question, there can be no grounds to stay the proceedings for failure to do so. If there was a breach of duty, there generally has to be either an element of bad faith, or at the very least some serious fault, on the part of the police or the prosecution authorities. Moreover, it has to be clear that the accused could not be fairly tried.
In many ‘missing evidence’ cases, the defence will be able to make use of the absence of that evidence, arguing that its absence should help to create a reasonable doubt in the minds of the jury or magistrates as to the guilt of the accused
The principles relevant to cases involving lost evidence were summarised in DPP v Fell  EWHC 562 (Admin), emphasising that a stay is to be granted only in exceptional cases.