Gather by old retreat in Scottish battlefield (8)
I believe the answer is:
culloden
'scottish battlefield' is the definition.
(I've seen this before)
'gather by old retreat' is the wordplay.
'gather' becomes 'cull' (culling is a kind of gathering).
'by' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'retreat' becomes 'den'.
'cull'+'o'+'den'='CULLODEN'
'in' is the link.
(Other definitions for culloden that I've seen before include "Butcher's success" , "Battle at which English defeated Bonny Prince Charlie" , "Scottish battlefield of 1746 where Jacobites were defeated" , "northern battleground" , "Last battle on British soil" .)