Interesting link there Britpete. Can’t seem to find prices though on the Esbjerg/Immingham route, noted that the sailings are at 21.30 every night which is helpful. Thanks. 
why not ask them what the cost will be
also ask for loaded and if there is a rebate for emptey
if you do not ask you will not get a answer
also if you get aprice of them you could look around and
see who uses this ferry a lot as to what price they might
give you,What about looking at a ticket brooker and ask t
hem what the price will be,