Brockwell is with wee Glaswegian getting mischievous (6)

I believe the answer is:

impish

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'mischievous' is the definition.
(synonyms)

'brockwell is with wee glaswegian' is the wordplay.
I cannot quite see how this works, but
'is' is found in the answer.
This explanation may well be incorrect...

'getting' is the link.

Can you help me to learn more?

(Other definitions for impish that I've seen before include "Playful" , "troublesome" , "Naughty" , "Wicked" , "Teasingly mischievous" .)

I've seen this clue in The Guardian.

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