The most common and most likely answer to this crossword clue is the 6 letter word BUGGED
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More clues leading to the result BUGGED
Buddy explains!

The straight part
We know that "Under surveillance/irritated" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case under surveillance/irritated = bugged.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 BUGGED mean?
BUGGED verb- To annoy.
- To install an electronic listening device or devices in.
- (on one's person or of a telephone line, dwelling, room, etc.) Containing a bug (interceptive listening device).
- (of software, website, feature, etc) Affected by a bug.