http://www.cps.gov.uk/legal/a_to_c/adverse_inferences/
What prevents Section 34 applying?
1- No adverse inferences can be drawn if the police have made up their mind to charge. Under the provisions of Code C paragraph 11.6, questioning must cease once the investigating officer/custody sergeant is of the view that there is a realistic prospect of conviction, and any interview after that point should not take place - Pointer [1997] Crim.L.R. 676. (But note that if the officer still has an open mind to the involvement or otherwise of the suspect, an interview can proceed even if there is clear evidence of guilt - Gayle [1999] Crim.L.R. 502, CA).
2- No adverse inference can be drawn if the case is so complex or related to matters so long ago, that silence would be justified as no sensible immediate response was appropriate.
3- No adverse inferences can be drawn if the facts in question were not known to the defendant at the time when he failed to disclose them. Nickolson [1999] Crim. L.R. 61. Refer to Pre-interview Disclosure below in this chapter.
4- No adverse inferences can be drawn unless legal advice is offered or made available from the initial stages of interrogation. This principle applies to terrorism cases. Murray (John) v UK (1996) 22 E.H.R.R. 29; Averill v UK [2001] 31 E.H.R.R. 3 and section 58 Youth Justice and Criminal Evidence Act 1999.
5- The language of section 34, (and subsections 36 and 37) indicate that adverse inferences cannot be drawn if the defendant faces trial on a different offence from that with which he was charged or given warning of prosecution (section 34) or which was originally specified when he was cautioned (section 36) or arrested (section 37). In the light of the charging program, such a situation should now be a rare occurrence.
6- A bare admission of facts in the prosecution case, or a mere suggestion or hypothesis are not facts relied on by the defence for the purposes of section 34. Betts and Hall [2001] 2 Cr.App.R. 16. Mere suggestion or hypothesis cannot be a foundation for adverse inferences. Nickolson [1999] Crim. L.R. 61.
When can Section 34 apply?
7- Adverse inferences can be drawn from failure to mention facts even though the police did not ask questions about all the charges eventually laid especially where the suspect could have made a note for his legal advisers. Napper [1996] Crim. L.R. 591, CA.
8- Adverse inferences can be drawn if there is a failure to mention a fact could relate to something said at a second or subsequent interview and which was not mentioned at the first interview. McLernon [1992] N.I. 168.
9- Adverse inferences can be drawn from failure to mention a fact later relied on even though it causes no surprise to the prosecution (Fox and Sullivan, unreported, 2.07.9). The defence can rebut allegations of recent fabrication by calling a third party to give evidence that the fact was disclosed at the time (usually the solicitor who attended at the police station).
10- Adverse inferences can be drawn even though the details of the fact relied on and not mentioned to the police, had been communicated to a third party. Taylor [1999] Crim.L.R. 77 CA.
11- The fact relied on need not be in the defendant's own evidence. Reliance can be through the evidence of other witnesses or even through cross-examination of prosecution witnesses or the defendant or his witnesses. Bowers [1998] Crim L.R. 817, CA and Webber [2004] UKHL1 is the most recent case to reiterate this point.
12- Adverse inferences can be drawn even when the truth or otherwise of the defendant's explanation for failure to mention the fact is the very question the jury has to decide in determining guilt. Hearne and Coleman [2000] 6 Archbold News 2, May 4. and Gowland-Wynn [2001] EWCA Crim 2715.
… IMO, a lot of wiggle room or gray areas remain for both Defence and Prosecution.