James v James  EWHC 43 (Ch)
"There is a preliminary question of law as to the test to be applied for testamentary capacity in a case like this, where the testator has made a will, died, and then the question of capacity has arisen. The traditional test for such a case is that laid down in Banks v Goodfellow (1870) LR 5 QB 549, 565, per Cockburn CJ: 'It is essential … that a testator shall understand the nature of his act and its effects; shall understand the extent of the property of which he is disposing; shall be able to comprehend and appreciate the claims to which he ought to give effect, and, with a view to the latter object, that no disorder of the mind shall poison his affections, avert his sense of right, or prevent the exercise of his natural faculties, that no insane delusion shall influence his will in disposing of his property and bring about a disposal of it which, if his mind had been sound, would not have been made.' ... More recently the Mental Capacity Act 2005 has made fresh provision for the law of mental capacity in certain situations. What is unfortunately not made express in that legislation is the extent to which this fresh provision affects the test for capacity to make a will when that question is being judged retrospectively (typically, though not necessarily, post mortem). ... The general rule of precedent, as applied in the High Court, is that that court is not strictly bound by decisions of co-ordinate jurisdiction, but will follow them as a matter of comity unless convinced they are wrong ... As it happens, I think the decision in Walker v Badmin  EWHC 71 (Ch)Not on Bailii [that the test in Banks v Goodfellow not only had survived the enactment of the 2005 Act, but that it, rather than anything in the Act, was still the sole test of capacity for judging will-making capacity in retrospect] is right, and for the reasons given by the deputy judge. ... Whilst it is a complication to have two tests for mental capacity in making wills, one prospective and the other retrospective, it is a complication created by the decision of Parliament to legislate as it has, a decision that the courts must respect."