Borough station tunnel size

[Deleted]

I don't know if CSLR has covered this yet, but am I the only one who thinks that the Borough station tunnels 'feel' smaller than station tunnels elsewhere on the Northern? I think the refurbishment of the station and the new lighting (why such dim lighting?!?) contribute a great deal to the feeling of smallness.

[CSLR]

I think this is an illusion, partly caused by the factors that you mention. The footbridge that cuts through the roof of the southbound tunnel helps to make that platform look even smaller.
The original station tunnels at Borough are the same size as those at Elephant & Castle, Kennington and Oval. At all four of these stations, the original brick station tunnels have been extended by slightly larger cast iron tunnels.