I felt that I could not investigate the cause of these two accidents without taking into consideration the other transformer failures, and also the troubles that had been experienced with other electrical equipment on the Glasgow suburban trains which may have had a bearing on the transformer failures. As the investigation proceeded it became essential to check the design of the transformers in use in trains on other sections of British Railways electrified on the high voltage A.C. system to ensure that they were immune from certain weaknesses discovered in the Glasgow transformers. It further became necessary to take note of the failures on the other recently opened high voltage A.C. electrified sections of British Railways to ascertain whether they and the transformer failures in the Scottish Region were in any way inter-related and, in particular, whether the introduction for the first time on any railway of a dual high voltage A.C. system had any bearing on the problem."