Brian Watson wrote:
Possibly the squeakiest tube line, though the Circle has its moments...

I'd also like to add the Waterloo & City, which I believe is (bar the
section of the Northern between Stockwell and somewhere south of London
Bridge) the oldest deep-level line on the network.

Just out of interest, I passed through Moorgate yesterday and noticed 2
terminating platforms (I think numnbers 3 and 4) between the Met/Circle
and Thameslink lines. What exactly are/were they for?