The most common and most likely answer to this crossword clue is the 14 letter word ANAESTHETISING
I've seen this crossword clue in The Sunday Telegraph
A
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Buddy explains!

The straight part
We know that "Working with numbers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case working with numbers = anaesthetising.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 ANAESTHETISING mean?
ANAESTHETISING verb- To administer anesthesia to: to render unfeeling or unconscious through the use of narcotic substances, usually either alcohol or pharmaceutical drugs.