British ship has space on board (6)
I believe the answer is:
embark
'board' is the definition.
(I know that embark is a type of board)
'british ship has space' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'ship' becomes 'ark' (I've seen this in other clues).
'has' says to put letters next to each other.
'space' becomes 'em' (in typography, a space as wide as a letter 'm').
'b'+'ark'='bark'
'bark' put after 'em' is 'EMBARK'.
'on' is the link.
(Other definitions for embark that I've seen before include "Start" , "get on board" , "Join ship" , "board production" , "Go on board, boat or plane" .)