Trade union golf club keeping old towing vessel (7)
I believe the answer is:
tugboat
'towing vessel' is the definition.
(I've seen this before)
'trade union golf club keeping old' is the wordplay.
'trade union' becomes 'TU' (abbreviation for trade union).
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'club' becomes 'bat' (as in sporting equipment).
'keeping' indicates putting letters inside (some letters kept inside).
'old' becomes 'o' (abbreviation).
'bat' placed around 'o' is 'boat'.
'tu'+'g'+'boat'='TUGBOAT'
(Other definitions for tugboat that I've seen before include "Powerful vessel used to pull larger ones" , "Drawing craft" , "Harbour craft" , "Ship pulling a larger one" , "Vessel towing larger vessels" .)