At Bank a few days ago, it could have been my eyes, but is the 420V* +ve 3rd rail still slightly higher than on erstwhile UERL lines (= 3" above top of running rail). (It might have been the superelevation on a curve, which decieved.( When I read that the conversion from 3rd to 3rd and 4th rail had taken place in 1940, I seem to recall some one mentioning the positioning of the outer current rail being problematic because of the constrained tunnel diameter. Is that the case? If it is, why was a link to the District laid in and then removed at Ealing Broadway? That part of the Ealing and Shepherd's Bush railway was built by the GWR with the 3rd rail in between the running rails in those days. The connection at Ealing must have been interesting both from the height of the power rails and their potential difference.
* Has the potential difference on the Central been uprated to 440+/220- or 500+/250- or something else?