He has some more in his own room, the devil! (5)

I believe the answer is:

demon

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'the devil' is the definition.
(synonyms)

'he has some more' is the wordplay.
'he' becomes 'den' ().
'has' indicates putting letters inside.
'some more' becomes 'mo' (I've seen this in other clues).
'den' enclosing 'mo' is 'DEMON'.

'in his own room' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for demon that I've seen before include "Fiend, devil" , "Fanatic; devil" , "Expert" , "Genius" , "Evildoer" .)

I've seen this clue in the Evening Standard.

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