A teach-in switching parts leaves much to be desired? (5,3)

I believe the answer is:

china tea

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'parts leaves much to be desired?' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'a teach-in switching' is the wordplay.
'switching' indicates anagramming the letters.
'a'+'teach'+'in'='ateachin'
'ateachin' is an anagram of 'CHINA TEA'.

Can you help me to learn more?

(Other definitions for china tea that I've seen before include "Eastern drink" , "cuppa?" , "Leaves for drink" .)

I've seen this clue in The Guardian.

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