Investment vehicle boss cracks before eggheads (7,5)
I believe the answer is:
premium bonds
'investment' is the definition.
(I've seen this before)
'boss cracks before eggheads' is the wordplay.
'boss' becomes 'umbo' (the boss on a shield).
'cracks' indicates putting letters inside (crack their way in).
'before' becomes 'pre' (prefix meaning 'before').
'eggheads' becomes 'minds' (I can't explain this - if you can you should give a lot more credence to this answer).
'pre'+'minds'='preminds'
'umbo' inserted into 'preminds' is 'PREMIUM BONDS'.
'vehicle' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for premium bonds that I've seen before include "Investment" , "investments" , "Connery and Craig in the minds of many?" , "Government securities that enter the holder for monthly cash prize draws" .)