Hi Julie,
How did you find the LD Lines service from Poole to Santander? I believe the ferry they are using is the Norman Asturias, we have used this on the Gijon to St Nazaire route and it was ....OK for an overnighter (14 hours) but the facilities were a bit limited compared to BFs Pont Aven plus when we went there were no kennels so the dogs had to stay in the car. If they have not installed kennels I imagine that they won't take dogs on this route.
I imagine that the fares would have to be much less than BF to make the Norman Asturias a possibility for this crossing.....its a bit small for the Bay of Biscay at this time of year.....especially when ferries the size of the Cap Finisterre have to run for port, as it did a few days ago.
At the moment it is sunny and 18degs in Asturias so not too much to complain about. Enjoy your stay in Portugal, I think you are having a better time of it than many back in the UK.
Happy New Year to everyone
regards
Phil & Jackie