Dim leader of Britain, a tragic figure (5)
I believe the answer is:
blear
'dim' is the definition.
(I've seen this before)
'leader of britain a tragic figure' is the wordplay.
'leader of' suggests taking the first letters.
'a tragic figure' becomes 'lear' (from Shakespeare's King Lear).
The first letter of 'britain' is 'b'.
'b'+'lear'='BLEAR'
(Other definitions for blear that I've seen before include "Indistinct" , "Blur" , "Make (the eyes) dim" , "Watery, blurred" , "Baler (anag.)" .)