A number of old party mandarins originally unlike old PM (5,2,6,5)
I believe the answer is:
knees up mother brown
'a number of old' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'party mandarins originally unlike old pm' is the wordplay.
I cannot really understand how this works, but
'party' could be 'kneesup' (knees-up means a party) and 'kneesup' is found in the answer.
'pm' could be 'brown' (I have seen 'Former PM ' mean 'brown' so perhaps 'pm' could also mean 'brown') and 'brown' is found within the answer.
The remaining letters 'mother' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?