As you may demand, is packed in tins (6)
I believe the answer is:
insist
'as you may demand' is the definition.
I can't judge whether this definition defines the answer.
'is packed in tins' is the wordplay.
'packed in' indicates putting letters inside.
'tins' becomes 'inst' (I can't explain this - if you can you should believe this answer much more).
'is' going within 'inst' is 'INSIST'.
Can you help me to learn more?
(Other definitions for insist that I've seen before include "express convinced viewpoint" , "Assert firmly" , "Demand forcefully" , "Take a firm stand" , "Take no refusal" .)