What happened with the GNR suburban electrification is that BR took over Finsbury Park - Moorgate from LUL and the Widened Lines then became redundant until further use was found for them.
Regarding the carriages, they were known as "Block Enders", Kings Cross suburban services were divided into inner, Welwyn Garden city/Hertford North to Kings Cross/Moorgate, and outer suburban, for example Stevenage, Letchworth, Baldock. The inner suburban rakes were composed of C's with a BS, and were also stabled at Hatfield, Potters Bar, Cuffley and Gordon Hill. They would make a morning peak run to Moorgate, ECS to yard such as Ferme Park, then reverse the journey for the evening peak.
The outer suburban rakes had at least a couple of carriages with gangways, toilets etc.
There was an Irish guard with a great sense of humour during the early 70's, one day he was grinning from ear to ear, he worked one of these units into Moorgate, and when one of the doors was opened, the hinges broke and the entire door fell onto the platform. So, as the unit was going to work ECS, he shoved the door into the compartment, while alerting the signalmen as to what was going on. Subsequentially, a BR official came with an "Out of Order" label, the question was where to put it
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