Fifty-one pence? What cheek! (3)

I believe the answer is:

lip

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'cheek' is the definition.
(both can mean insolence or rudeness)

'fifty-one pence?' is the wordplay.
'fifty' becomes 'l' (roman numeral).
'one' becomes 'i' (roman numeral).
'pence?' becomes 'p'.
'l'+'i'+'p'='LIP'

'what' acts as a link.
This may not be correct. It may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for lip that I've seen before include "Impudent talk from part of the face" , "Rim of an orifice" , "giving such insincere service" , "Rim; impertinence" , "Brink" .)

I've seen this clue in the Evening Standard.

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