Cryptic crossword clue
What you’d see in London street once, but not everywhere 4

Buddy explains!

The straight part

We know that "once, but not everywhere" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case once, but not everywhere = onst.

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.