He lacks a full can, when paint is spilt (7)

I believe the answer is:

captain

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'he lacks a full' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

'when paint is spilt' is the wordplay.
'when' becomes 'ca' (I can't justify this - if you can you should give a lot more credence to this answer).
'is spilt' is an anagram indicator.
'paint' anagrammed gives 'ptain'.
'ca'+'ptain'='CAPTAIN'

'can' is the link.

Can you help me to learn more?

(Other definitions for captain that I've seen before include "Naval commander" , "Skip" , "Commander of a ship" , "soldier" , "Chief" .)

I've seen this clue in the Evening Standard.

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