The most common and most likely answer to this crossword clue is the 8 letter word ENFORCED
I've seen this crossword clue in The Daily Telegraph
E
N
F
O
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C
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D
More clues leading to the result ENFORCED
Buddy explains!

The straight part
We know that "Imposed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case imposed = enforced.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 ENFORCED mean?
ENFORCED verb- To keep up, impose or bring into effect something, not necessarily by force.
- To give strength or force to; to affirm, to emphasize.
- To strengthen (a castle, town etc.) with extra troops, fortifications etc.
- To intensify, make stronger, add force to.
- To exert oneself, to try hard.
- To compel, oblige (someone or something); to force.
- To make or gain by force; to force.
- To put in motion or action by violence; to drive.
- To give force to; to strengthen; to invigorate; to urge with energy.
- To urge; to ply hard; to lay much stress upon.
- To prove; to evince.