"Recliner" wrote

As I recall, Wembley and the two Sudbury stations were four-tracked (two
through lines, two platform lines), but there was only double track
between the stations. Re-instating that arrangement would make it easier
to have more stoppers at those three stations (not something Chiltern
favours), but wouldn't do much for the overall capacity.

IIRC that was the arrangement at all stations between Wembley Hill and
Princes Risborough (both inclusive), with the exceptions of Denham Golf
Club, Seer green, and Saunderton. The only 4-track section was from Northolt
Junction to West Ruislip. Is it still the case that, if an all-stations
train is let out of Marylebone immediately in front of a fast, the fast
can't overtake until Princes Risborough?

Peter