Quite by chance I have a copy of the snappily titled Second Interim Report on the Accidents and Failures which occurred in Multiple Unit Electric Trains in the Scottish Region and Eastern Region British Railways.
While this largely concentrating on the problems with the Eastern's GEC-equipped units (later Cl305) on the "NE London Suburban Electrified Lines" (or the West Anglia routes, as we call it today), it also makes mention of progress made towards modifications with Scotland's AEI-equipped units (later Cl303). This document is dated 30 May 1961 and refers to "accidents" on 13 and 17 December 1960, the last of which resulted in a withdrawal of the entire Glasgow suburban electric fleet, and to an interim report dated 13 January 1961 in which the causes of the failures were established and the work to be done to rectify them was outlined.
While the traction equipment was different on each fleet there appears to have been a number of common issues, specifically when operating on the 6.25kV AC OLE. Both fleets suffered transient over-voltages that caused some similar and some different problems. As well as better ventilation to deal with problems with the mercury arc rectifiers and the need to fit better surge suppression to protect the motors, the Glasgow units required a full transformer re-build as it was found that "...excess current conditions had caused the collapse of the original transformer secondary windings".
As at 3 May 1961, 68 AEI transformers had been rebuilt to the new specifications with 32 modified units having been delivered back from the Dukinfield Railway Works near Manchester for trial running and driver training. A test train comprising two modified units kitted out as a mobile laboratory had been run successfully over the nights of 21, 22 and 23 March 1961 and was planned to run for a total of 20000 miles. Each modified unit was also required to run for 2000 miles before being returned to service.
In Glasgow there was little alternative but to return to steam operation, but on the NE London suburban lines the troublesome GEC units were relegated to the Chingford line and the Colchester-Clacton line where any failures would not cause massive knock-on delays, while the electric service was propped up by diverting English Electric units intended for the London, Tilbury & Southend electrification scheme and from the Colchester-Clacton line (probably a mix of Cl302's and Cl308's).
Quite how this story ends I cannot say because I have not seen the promised final report. However, it appears that your visit must have coincided with this saga.
O L Leigh
