Person who offers to hold case for cockney traveller (8)
I believe the answer is:
gulliver
'cockney traveller' is the definition.
'gulliver' can be an answer for 'traveller' (I've seen this before). I'm not sure about the 'cockney' bit.
'person who offers to hold case' is the wordplay.
'person who offers' becomes 'giver'.
'to hold' is an insertion indicator.
'case' becomes 'ull' (I can't justify this - if you can you should give a lot more credence to this answer).
'giver' going around 'ull' is 'GULLIVER'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for gulliver that I've seen before include "Swift man" , "Dean Swift's travelling man" , "Lilliput visitor" , "Dean Swift's fictional traveller" .)