Crooked thief's protecting fool that's lifted sandwich spread (4,5)

I believe the answer is:

fish paste

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'sandwich spread' is the definition.
(you might have fish paste in a sandwich)

'crooked thief's protecting fool' is the wordplay.
'crooked' is an anagram indicator (a crooked or disrupted version of the letters).
'protecting' means one lot of letters goes inside another (inserted letters are held or protected).
'fool' becomes 'pas' (I am not sure about this - if you are sure you should believe this answer much more).
'thiefs' with letters rearranged gives 'fishte'.
'fishte' placed around 'pas' is 'FISH PASTE'.

'that's lifted' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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