Huge flow of gold found in British river (7)
I believe the answer is:
torrent
'huge flow' is the definition.
'gold found in british river' is the wordplay.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'found in' indicates putting letters inside.
'british river' becomes 'trent' (English river).
'or' put into 'trent' is 'TORRENT'.
'of' acts as a link.
(Other definitions for torrent that I've seen before include "Heavy flow of water" , "Host" , "Fast-moving stream" , "A rushing stream of water" , "Outburst" .)