Simple band from London line left at the end (7)
I believe the answer is:
circlet
'simple band' is the definition.
'london line left at the end' is the wordplay.
'london line' becomes 'circle' (London Underground line).
'at the end' suggests the final letters.
The final letter of 'left' is 't'.
'circle'+'t'='CIRCLET'
'from' is the link.
(Other definitions for circlet that I've seen before include "Ornamental headband" , "Small round shape" , "Diadem" , "Metal band" , "Little hoop" .)