In message , at 15:32:02 on Sun, 25
Feb 2007, Steve Fitzgerald ] remarked:
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.

Sounds plausible, and perhaps this one key works all the trains? Now,
the topic that got us started here was the possibility of having to move
a train that was blocking the line, and that this would be impossible
without the right key [1]. It seems fairly obvious that the crew
piloting the escape train would have been given a set of keys for just
this eventuality.

[1] I have always said that such trains were unlikely to be found, but
someone else started this particular rathole.
--
Roland Perry