Former Prime Minister: "I am rubbish at Chinese" (5,4)

I believe the answer is:

imran khan

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'former prime minister' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'i am rubbish at chinese' is the wordplay.
'i am' becomes 'I'm' (contraction).
'rubbish at' becomes 'rank' (I can't explain this - if you can you should give a lot more credence to this answer).
'chinese' becomes 'han' (Chinese dynasty).
'im'+'rank'+'han'='IMRAN KHAN'

Can you help me to learn more?

(Another definition for imran khan that I've seen is " politician in Pakistan".)

I've seen this clue in The Independent.

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