Speculate minister will overturn tariff of fish or lamb but not squid or snail (10)
I believe the answer is:
'fish or lamb but not squid or snail' is the definition.
I can't judge whether this defines the answer.
'speculate minister will overturn tariff' is the wordplay.
'speculate' becomes 'bet' (I've seen this in other clues).
'minister will' becomes 'rev' (I am not sure about this - if you are sure you should believe this answer much more).
'overturn' says the letters should be written backwards.
'tariff' becomes 'rate' (I've seen this before).
'betrev' reversed gives 'verteb'.
'of' is the link.
Can you help me to learn more?
(Another definition for vertebrate that I've seen is " One with backbone".)