-
Technically you can take bike if partly dissamblied, even on the Undergroujd.
Technically I think the rule on British railways is "baggage must fit within a 1m x 1m x 1m space" and that applies at peak hours on trains and all the time on "deep stations" on the underground.
That is what permits folding bikes, and I find the 1m3 rule a lot easier to understand than the "this bike yes, that bike no" stuff.
Technically you can take bike if partly dissamblied, even on the Undergroujd.