Passage by sea, said ghastly cockney lifesaver, Romeo (8)
I believe the answer is:
corridor
'passage' is the definition.
(passage in a building)
'sea said ghastly cockney lifesaver romeo' is the wordplay.
'said' indicates a 'sounds like' (homophone) clue.
'ghastly cockney' becomes ''orrid' ('horrid' - I've seen this in another clue - said with a cockney accent, dropping the 'H').
'lifesaver romeo' becomes 'or' (I can't explain this - if you can you should give a lot more credence to this answer).
'sea' is a homophone of 'c'.
'c'+'orrid'+'or'='CORRIDOR'
'by' acts as a link.
Can you help me to learn more?
(Other definitions for corridor that I've seen before include "Passageway in building" , "Passage connecting rooms" , "Passageway between rows of offices" , "Indoor passage" , "way through" .)