North London line did use the 501’s until the 313’s came along. Never got a train into Broad Street station, although I do remember the station before it closed.
I had moved down from Manchester where most of our local trains were noisy/smelly first generation DMU’s.
Yes and no re 501 vs 313. Although more modern the seats on the 501 were much more comfortable compared to the very thin 313. However I hear the 700 and similar ironing board seats are even worse.
Yes it was basically dodgy builders. Some of the tunnels were built with less brick rings than needed, this led to some collapses and resulted in extra rings having to be built. As a result this restricted the loading gauge, and hence the need for dedicated stock.
In the 1980s some of the tunnels were singled tracked which allowed normal stock to use the line.
BR had the 33/2 and the 201,202 and 204 DEMU built especially for the line. About 11 inches narrower than standard stock.
Believe it when I see it. It would have to be much cheaper than Eurostar, but have decent frequency to attract passengers. Just can’t see that happening. Also suspect SNCF who I think own most of Eurostar have deep enough pockets to kill any new supplier with a deep discounting.