The steam locos used by the GWR▸ were condensing engines based at OOC▸ .
But they didn't condense all the time

The equipment made the locos very difficult to drive and so drivers regularily didn't condense.
The main problem with condensing is that it heats the water in tanks and makes the injectors difficult to operate. As injectors are the most vital part of a steam loco, apart from Brakes, if they fail the fire has to be thrown out. Which would not be easy on a four rail elecctrified line Underground!
Ex
LM▸ Fowler 2-6-2s and ex GN N2's could condense to Moorgate on the widened lines.