Nemo judex in re sua is both an ancient and fundamental principle of English law. A judge is disqualified from determining any case in which he or she may be, or may fairly be suspected to be, biased. The word ‘bias’ comes from the tendency of a bowl to turn in one direction of another. It thus means simply an improper predisposition of a judge to decide in one way or another. But if the fundamental nature of the rule is well recognised, its application and reach is less clear. The law is set about by some subtle distinctions which have been unstable and uncertain in the recent past. The law is now relatively clear, but the way in which it is applied is still open to debate and discussion. A person is barred from deciding any case in which he or she may be, or may fairly be suspected to be, biased. This principle embodies the basic concept of impartiality and applies to courts of law, tribunals, arbitrators and all those having the duty to act judicially. A public authority has a duty to act judicially whenever it makes decisions that affect people\'s rights or interests, and not only when it applies some judicial type procedure in arriving at decisions. that affect people\'s rights or interests, and not only when it applies some judicial-type procedure in arriving at decisions. The basis on which impartiality operates is the need to maintain public confidence in the legal system . The erosion of public confidence undermines the nobility of the legal system, and leads to ensuing chaos. It was held He should not have sat. It was accepted that he had had no pecuniary interest himself, and had acted scrupulously. It was a question of whether there was any appearance of bias. The essence of the need for impartiality was observed by Lord Denning, the Master of the Rolls, in Metropolitan Properties Co.(F.G.C.) Ltd. v. Lannon (1968) ‘Justice must be rooted in confidence and confidence is destroyed when right-minded people go away thinking \'The judge was biased.’ Besides, Lord Denning MR considered the test for apparent bias, and said ‘The court looks at the impression which would be given to other people. Even if he was as impartial as could be, nevertheless if right-minded persons would think that, in the circumstances, there was a real likelihood of bias on his part, then he should not sit. And if he does sit, his decision cannot stand.’

Public confidence as the basis for the rule against bias is also embodied in the often-quoted words of Lord Hewart, the Lord Chief Justice of England and Wales, that
‘It is not merely of some importance, but of fundamental importance that justice should not only be done, but should manifestly be seen to be done’

It was stated in an article , that Article 6(1) of the European Convention of Human Rights and Fundamental Freedoms 1950 as incorporated in the Human Rights Act 1988, applicable in England since 2000 provides that in the determination of his civil rights and obligations to everyone is entitled to a fair hearing by an independent and impartial tribunal established by law. The independence of courts and impartiality of judges are closely related in that they operate to sustain public confidence in the administration of justice.

The twin domestic UK law concepts of actual and apparent bias have their parallel in European law in the recognition by the European Court of Human Rights (ECHR) and the European Court of Justice (ECJ) that there are two aspects to the requirement of impartiality, subjective and objective impartiality. Subjective impartiality means that the members of the tribunal themselves must be subjectively impartial, none of its members must show bias or personal prejudice, there being a presumption of personal impartiality in the absence of evidence to the contrary. Objective impartiality requires the tribunal to “offer guarantees sufficient to exclude any legitimate doubt in this respect” .

Broadly speaking, the ECHR and the ECJ appear to have had less difficulty with the practical application of these concepts than the domestic UK courts. It was stated in an article, Bias by Holly Shout that in a particular, the concept of apparent bias has proved especially difficult to apply in practice,