A revolution in a country is complete in law as soon as its courts hold the new regime to be lawful. If such recognition is delayed, those in power may wax impatient but they know only too well the advantage which the seal of legality carries. In this way is the stage set for a game of manoeuvre between the courts and the rebels, as happened in Rhodesia.

The beginning of the sixteenth century saw a grave constitutional conflict, ending in a revolution—a conflict and revolution in which lawyers became principal actors. “In the hands of Coke the Common Law forged the axe which beheaded Charles I.” Dr. Cowell, Master of Trinity Hall from 1598 to 1611, played a leading part in that conflict—though on the losing side.

The criminological positivists at the turn of the century started a good deal of creative rethinking about the criminal law. Some of their proposals have gained widespread acceptance in the criminal law as we know it today. Others made no headway at all. One particular proposal, and a very fundamental one indeed, began a controversy which has ebbed and flowed regularly since. That is the proposal to eliminate from the criminal law the whole apparatus of substantive principles, or at least some of them, such as the legal insanity defence, which owe their presence to the law's traditional concern for distinguishing the guilty and the innocent in terms of their blameworthiness. The essence of the proposal is that innocence in this sense, moral innocence, if you will, should not disqualify a person from the consequences of the penal law. Moral innocence should, it is urged, give way to social dangerousness as the basis for a criminal disposition.

The concern of this article is twofold. In the first place it seeks to question the weight and value of the authority upon which the House of Lords in Selvey v. Director of Public Prosecutions purported to found the existence of a judicial discretion to exclude, in a criminal trial, evidence which is both relevant and admissible, on the ground that it is prejudicial to the accused. Secondly, it seeks to evaluate the contribution which such a discretion has made and is likely to make to the theory and practice of the law of evidence.