In message , Clive Coleman.
writes

Trains have keys? Where do they fit - in the side of the steering
column?

Yes trains at least did have keys and I would expect still do. I have
a set of keys for 38/62 stock, for the old 800s and 63xxs and also a
key for unlocking the desk on Brush, EE, and Crompton locomotives. I
don't know but I have no reason to suspect the use of keys to have
changed.

LUL trains have a key to open up the controller or reverser. Known as
an RKL220 key as that's the number on the key. It's also part of the
safety procedures as you shut down your train and hand over your RKL220
key to provide protection to staff on the track.

73 stock (at least) also have a Control Key (which looks something like
a spanner) to open up the cab.
--
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