Within one's powers, a leader in Britain cutting social security (6)
I believe the answer is:
doable
'within one's powers' is the definition.
I can't judge whether this defines the answer.
'a leader in britain cutting social security' is the wordplay.
'leader in' indicates taking the first letters.
'cutting' indicates putting letters inside (some letters cut their way into a word).
'social security' becomes 'dole' (I can't explain this - if you can you should give a lot more credence to this answer).
The initial letter of 'britain' is 'b'.
'a'+'b'='ab'
'ab' put inside 'dole' is 'DOABLE'.
Can you help me to learn more?
(Other definitions for doable that I've seen before include "Able to be carried out" , "Achievable, performable" , "possible" , "easy to achieve" .)