Ritaratbag wrote on Feb 11^th, 2014 at 8:25am:

Brittany Ferries new economy service will offer weekend crossings, between Portsmouth and Santander. During the week they will be carrying freight only. Passengers will be offered a limited catering service, and basic en suite cabins will be available. One way fares this Spring will start at £79 to France and £169 to Spain which includes two reclining seats. To check and for further info. see their web site.

I've been to their website and I can't see anything near that cheap between Portsmouth and Santander.  The cheapest they are offering on their website from Portsmouth to Santander is £229 for two people with a car and sleeping in reclining seats. Do you have a link to this offer?