The most common and most likely answer to this crossword clue is the 10 letter word ESCALATORS
I've seen this crossword clue in Independent
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Buddy explains!
The straight part
We know that "The ups and downs of many a London commuter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the ups and downs of many a london commuter = escalators.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ESCALATORS mean?
ESCALATORS noun- Anything that escalates.
- A motor-driven mechanical device consisting of a continuous loop of steps that automatically conveys people from one floor to another.
- An upward or progressive course.
- An escalator clause.