Strained party ends without regulars (8)
I believe the answer is:
laboured
'strained' is the definition.
('laboured' can be a synonym of 'strained')
'party ends without regulars' is the wordplay.
'party' becomes 'labour' (Labour Party is an example).
'without regulars' means one should take alternating letters (letters must be removed at regular intervals).
The alternate letters of 'ends' are 'ed'.
'labour'+'ed'='LABOURED'
(Other definitions for laboured that I've seen before include "Showing great effort" , "work lacking fluency" , "Travailed" , "far from fluent" , "Produced" .)