Joint effort left British overseas without leaders (5)
I believe the answer is:
elbow
'joint' is the definition.
(elbow joint is a kind of joint)
'effort left british overseas without leaders' is the wordplay.
'leaders' indicates taking the first letters.
The initial letters of 'effort left british overseas without' is 'ELBOW'.
(Other definitions for elbow that I've seen before include "Dismissal?" , "Sharp bend in a road or river" , "Barge" , "part of the body" , "Major arm joint" .)