Date of this Version
The general principle in common law jurisdictions is that relevant evidence is admissible, unless it falls within a category which is excluded by law, or it is excluded inthe exercise of a recognized judicial discretion. If evidence falls within a legally excluded category, it is excluded irrespective of general factors that may favor its admission (such as the public interest in convicting the guilty), unless it falls within an exception to the exclusionary rule (eg hearsay is generally excluded but certain hearsay statements such as admissions are not).
In the English tradition illegally or improperly obtained evidence was not a category of evidence excluded by operation of law, and was thus admissible, whatever its character (eg whether brought into existence by the illegality or not). However, such evidence could be excluded even though relevant by the coua in the exercise of its general faimess discretion. This fairness discretion focused primarily on exclusion of unreliable evidence and was thus rarely if ever exercised in relation to illegal real evidence, as opposed to confessional evidence. Evidence could he classed as illegal by reference to the ordinary law applicable to its obtaining, or, mostly where it was confessional in nature, as improperly obtained, ie given voluntarily hut in circumstances where conduct by the authorities later judged improper resulted in the relevant statement being made.
In more recent times most of the common law jurisdictions have abandoned sole reliance on the fairness discretion and have developed discreet rules and discretionary powers concerning admission or exclusion of illegal and improper evidence, with human rights provisions becoming the main reference frame for determining admissibility.