The rule against receiving evidence from jurors about jury deliberations is not absolute; a court may receive such evidence in exceptional circumstances, but only where, if the alleged irregularity were established, the verdict would be set aside despite the proviso. The threshold for ordering an inquiry into jury misconduct requires the court to be satisfied that the proviso could not save the verdict — that is, that there is a significant possibility that an innocent person has been convicted. Peripheral extrinsic information (such as relative costs of transport or goods) introduced into the jury room will not ordinarily warrant inquiry or vitiate a verdict.
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