It is very easy to find oneself on a tube platform with a group of
potential assailants positioned between oneself and the exit. In such
situations the only means of escape, should the group turn hostile,
would be across the tracks to the neighbouring platform.

What is the recommended method of crossing tracks in these situations?

There seem to be a variable number of rails making up the tracks,
usually about 5. Which of these are 'live'?

Will stepping on a live rail result in immediate death? What is the
safe distance from a live rail? Is it safe to tread on a live rail
with only one foot with the other in the air, in order to avoid
earthing the current?