Fairly clever Brits high on drugs (9)

I believe the answer is:

brightish

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'fairly clever' is the definition.
I can't tell whether this definition defines the answer.

'brits high on drugs' is the wordplay.
'on' means one lot of letters go next to another.
'drugs' indicates an anagram (I've seen 'drugged' mean this).
'brits' put after 'high' is 'highbrits'.
'highbrits' with letters rearranged gives 'BRIGHTISH'.

Can you help me to learn more?

(Another definition for brightish that I've seen is " Fairly intelligent".)

I've seen this clue in The Independent.

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