Kev wrote:

In that case I don't understand where you are going to put it so that
it doesn't get in the way.

Just below roof height on the partition separating the seats from the
walls, on the seat side? Or maybe (lateral thinking) on the station
platforms.

Anyhow, it'd be a better concept on trains, especially intercity ones.

Most tube trains that I get on are nose to
nose. Anything that you put in will take up space, unless it hangs from
the roof then space is limited.
I would like to see them banned along with the other scurge of the
underground, bottled water.

Precisely what adverse effect does someone consuming bottled water (or
indeed any other drink) have on your Tube use?

Neil