Demand 150, an excellent figure (5)

I believe the answer is:

claim

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'demand' is the definition.
(I know that claim is a type of demand)

'150 an excellent figure' is the wordplay.
'a50' becomes 'CL' (Roman numerals).
'an excellent figure' becomes 'aim' (I can't explain this - if you can you should give a lot more credence to this answer).
'cl'+'aim'='CLAIM'

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(Other definitions for claim that I've seen before include "Assertion of ownership etc" , "Assertion of right" , "title" , "Put in for" , "Allegation" .)

I've seen this clue in the Evening Standard.

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