Former PM succeeded, with happy attitude all round (9)
I believe the answer is:
gladstone
'former pm' is the definition.
(I've seen this before)
'succeeded with happy attitude all round' is the wordplay.
'succeeded' becomes 's' (genealogical abbreviation).
'with' means one lot of letters go next to another.
'happy' becomes 'glad' (synonyms).
'attitude' becomes 'tone' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'all round' indicates putting letters inside.
'glad' put next to 'tone' is 'gladtone'.
's' going into 'gladtone' is 'GLADSTONE'.
Can you help me to learn more?
(Other definitions for gladstone that I've seen before include "Old English P.M. or a doctor's bag" , "Bag for a former British statesman" , "British statesman, four times PM, d. 1898" , "Liberal leader" , "Former English PM or kind of bag" .)