Awfully unimportant: a UK leader in crisis — stop perhaps? (11,4)
I believe the answer is:
punctuation mark
'stop perhaps?' is the definition.
(stop is a kind of punctuation mark)
'awfully unimportant a uk leader in crisis' is the wordplay.
'awfully' indicates anagramming the letters.
'leader in' suggests taking the first letters.
The first letter of 'crisis' is 'c'.
'unimportant'+'a'+'uk'+'c'='unimportantaukc'
'unimportantaukc' anagrammed gives 'PUNCTUATION MARK'.
(Other definitions for punctuation mark that I've seen before include "period in US, say" , "period in New York, perhaps? - with 5d" , "Possibly stop" .)