R v Denham & Anor  EWCA Crim 1048
This case centred aroung a criminal appeal against conviction where the Crown Court judge had allowed an application to adduce previous other convictions relating to co-conspirators under s.74 Police and Criminal Evidence Act 1984.
The approach adopted in best summarised in the extract below, lifted directly from the judgement:
He accepted that s.74 should not be used to allow evidence to go before a jury which is irrelevant, inadmissible, prejudicial or unfair simply because it was convenient for the jury 'to have the whole picture'. He directed himself in accordance with the law as set out in Derek Nathan Smith at .
It remains a proper approach, we are satisfied, that where there was no real question that the offence was committed by someone and the real issue was whether the present defendant was a party or not, the evidence of pleas of guilty is likely to be perfectly fair, though each case depends on its own facts.
He also noted the court's qualification to that general proposition, namely:
However, it also remains true that such evidence may well be unfair if the issues are such that the evidence closes off issues which the jury has to try.'
The judge adopted that approach at p.9D of his ruling.
If the admission of the guilty pleas of others effectively shuts down a defence, or a particular line of defence, or makes it a practical impossibility to defend the case, then the pleas must not, of course, be admitted.
Having reviewed the authorities the judge concluded (at 10F):
Section 74 is to be approached with caution and it is not to be used as a matter of routine. It is not to be used as a smuggling device to place evidence before the jury which it would be convenient for the jury to hear. The paradigm notions to be applied will be those of relevance and then fairness.