One is up to one's neck resolving car tax (6)
I believe the answer is:
cravat
'one is up to one's neck' is the definition.
I can't judge whether this defines the answer.
'resolving car tax' is the wordplay.
'resolving' indicates anagramming the letters.
'tax' becomes 'vat' (UK Value Added Tax).
'car' is an anagram of 'cra'.
'cra'+'vat'='CRAVAT'
Can you help me to learn more?
(Other definitions for cravat that I've seen before include "Neckerchief" , "leisure-wear" , "Item of neckwear" , "Strip of fabric worn round the neck" , "An elaborate or fancy tie - Beau Brummel wore one" .)