Paul Stevenson writes
How will this fit in with the byelaw preventing the use of radios and
personal stereos on the UndergrounD?

There is no such byelaw. However there is a byelaw which says that
no-one is allowed to use equipment for the reproduction of sound "to the
annoyance of any person" - which is slightly different.

So using a stereo with decent headphones is perfectly legal.

--
Dave