The most common and most likely answer to this crossword clue is the 7 letter word HANDLER
I've seen this crossword clue in The Sunday Telegraph
H
A
N
D
L
E
R
More clues leading to the result HANDLER
- Dog trainer's assistant runs after large poodle ultimately
- Dogged policeman?
- Police employee US writer caught out
- Agent losing old retailer’s capital
- Worker taken on by king, not a good person for Rex?
- Raymond caught absconding seeing policeman with dog
- Raymond heading off to become dog trainer?
- Person in charge of dog with name Rex
- Spy usually has one name, right?
- Hard-boiled novelist’s lost first letter M, perhaps?
Buddy explains!

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 HANDLER mean?
HANDLER noun- One who handles something (especially manually) or someone.
- (in combination) A controller, trainer, someone who handles a specified thing, animal or person (especially a prizefighter).
- An advisor or manager to a person occupying a position or office to which the speaker believes the holder does not possess the typical qualifications and/or experience.
- A subroutine that handles a particular situation such as an event or exception.