Cockney's steering wheel of timber (3)
I believe the answer is:
elm
I believe this is a double definition.
'cockney's steering wheel' is the first definition.
('helm' - I've seen this before - said with the 'H' dropped - a cockney accent.)
'timber' is the second definition.
(I've seen this before)
'of' acts as a link.
(Other definitions for elm that I've seen before include "Species of tree" , "Victim of fungus" , "Leaving body" , "Kind of tree" , "I branch out" .)