On 01/07/2016 16:04, whisky-dave wrote:
even the underground trains aren't standardised are they.
You have specific ones for specific lines.

Central line, for example, definitely uses smaller rolling stock than
most (all?) other LU lines.

But on occasion mainline BR rolling stock has been run through some of
the LU system. One example was a track recorder coach which they ran in
the 1970s - apparently it only caused a tiny bit of damage (to itself or
to the tunnels).

--
Rod