Clubs twice invested in shabby old kit for assembly (7)
I believe the answer is:
meccano
'kit for assembly' is the definition.
(Meccano is a toy for assembling models)
'clubs twice invested in shabby old' is the wordplay.
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'twice' shows that letters should be duplicated.
'invested in' means one lot of letters goes inside another.
'shabby' becomes 'mean' (both can mean unkind or unfair).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'c' duplicated is 'cc'.
'cc' placed into 'mean' is 'meccan'.
'meccan'+'o'='MECCANO'
(Other definitions for meccano that I've seen before include "constructive materials" , "Metal model construction set" , "Set of metal components for making toy models" , "Children's nuts and bolts kit" , "It's for kids' building" .)