The most common and most likely answer to this crossword clue is the 11 letter word HORSE-DRAWN
I've seen this crossword clue in The Guardian
H
O
R
S
E
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D
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Buddy explains!
The straight part
We know that "Like the Queen’s coach" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case like the queen’s coach = horse-drawn.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 HORSE-DRAWN mean?
HORSE-DRAWN adjective- (of a vehicle) Pulled along by one or more horses.