Taking your own drinks onto Brittany Ferries?

Hi, we have just come back from a trip to Amsterdam as foot passengers on a P and O ferry and were surprised to find that we weren't allowed to take our own bottle of wine on board, to enjoy in our cabin. We are booked on the Pont Aven with our car and caravan in a couple of weeks, Portsmouth to Santander. Does anyone know if the same rules apply? I am guessing not, as surely they don't search everyone's overnight bags on the way up from the car deck? We just want to keep the costs down a bit - we aren't alcoholics! Looking at the menus, etc it looks like they do charge top rates to their captive consumers for 24 hours. We may also take a freezer bag with a picnic, etc. We haven't been on this route before, so any tips would be welcome.