People persist in saying "disinterested" when what they mean is "uninterested". These words are actually quite different.
In the first word, having an "interest" in something has the eighteenth-century meaning of having a "stake" in it. Thus, if I am watching a game of football, if I have no commitment to either side (such as a bet on the result, or support for my local team), I am disinterested in the result; but if I hate football and couldn't care less who wins, then I am merely uninterested. The referee must be disinterested (that is, unbiased), but if he was uninterested he would be no use at all.
The principle of British justice is that the judge and jury must be disinterested: without prior commitment or bias to either side; and juries are carefully selected to this end. This has not always been the case: in previous centuries, judges were seen as "lions under the throne", whose job was to help secure the conviction of the King's enemies, and made little pretense of being disinterested; Judge Jeffreys in the later seventeenth century being a notorious example. Judicial disinterest seldom applies under dictatorships; one need only cite the "revolutionary justice" of Soviet Russia, particularly under Lenin and Stalin, and of the tribunals in the "Terror" of 1793-4 of the French Revolution. But,once again, a judge at any time and in any type of court who was uninterested in the case before him would be useless.
It was a classic Marxist argument that the promise of "disinterested justice" would always be a sham: class interest is all-pervasive. I wonder if the recent demand in Britain for more judges from the racial minorities, and fewer from the elite independent schools and universities, is based upon the notion that judges from privileged and rich backgrounds are unlikely to be truly disinterested? Or, more likely, that they may not be perceived as being disinterested?