All - as an AA member I can get a discount on fares on both Stena and Irish Ferries. It used to be something like 5%, but now they don't publish the exact rate on the web and you have to call to find out.
I also used to be able to get a discount for using a particular credit card I used to have, but that scheme seems to have been abolished.
I have a feeling that AMEX Blue did a promotion with Stena a while ago, but I can't remember exactly.
Does anyone know of any other generally available (but little known) discount schemes specifically for ferries to the UK ?
z