Tribunal of Commissioners 25 November 2005
Case Nos CDLA/2879/2004 and CDLA/2899/2004
7.Evaluating the disability that arises from medically unexplained symptoms in an individual case may be even more difficult. It is likely in such cases that physical examination will be normal and that special investigations such as scans, blood tests etc. are normal. The fact that no definite pathological basis for the symptom has been identified to date does not mean that one does not exist, or that the symptom has no physical basis whatsoever.
8.In many cases where there is a clear physical cause for disabling symptoms psychological factors may come into play. Indeed such factors may be the main reason for much of the disability observed. ….”
109.On the basis of this evidence, Mr Maurici submitted in his skeleton argument:
“Where a claimant’s inability or virtual inability to walk is caused by a combination of physical and mental factors the bottom line is that in many cases it is not possible in terms of medical analysis to separate the factors out in order to determine which is the effective cause of the inability or virtual inability to walk.”
110.We are satisfied that the analytical exercise required by the three tests of causation we have referred to (including the “but for test”) would in most cases be unrealistic in that the decision maker or tribunal would not have evidence which would be necessary to enable the analysis sensibly to be carried out. Mr Kolinsky and Mr Maurici each submitted, in our judgment with compelling force, that Parliament could not have intended a test for causation which would often be incapable of practical application.
111.They each submitted that the following test would be both consistent with the statutory language and as workable as reasonably possible: the claimant’s physical condition must be a material cause of his inability or virtual inability to walk, and it will be a material cause if it contributes to his inability or virtual inability to walk to any appreciable extent - i.e. to any extent which is more than de minimis.
112.Mr Maurici sought to support this submission by reference to authorities taken from the law of tort in which the “but for” test for causation was departed from, and in particular the decision of the House of Lords in Bonnington Castings Ltd v Wardlaw  AC 613. In that case the plaintiff contracted pneumoconiosis from inhaling air at his workplace that contained silica dust. The main source of the dust was from pneumatic hammers in respect of
“[T]he medical evidence was that pneumoconiosis is caused by a gradual accumulation in the lungs of minute particles of silica inhaled over a period of years. That means, I think, that the disease is caused by the whole of the noxious material inhaled and, if that material comes from two sources, it cannot be wholly attributed to material from one source or the other.”
On that basis Lord Reid considered that:
“… the real question is whether the dust from the swing grinders materially contributed to the disease. What is a material contribution must be a question of degree. A contribution which comes within the exception de minimis non curat lex is not material, but I think that any contribution which does not fall within that exception must be