I did read that P&O couldn't find a suitable replacement vessel for the Pride of Bilbao, hence the decision to scrap the route, but that strikes me as odd that they would look for a replacement ship for a loss-making route unless the current ship herself is one of the reasons for the route losing money (older ship, more costly to maintain, etc?).
Brittany Ferries do a Spanish route, but that is Plymouth-Santander so I wonder if they would fill the gap left by P&O at Portsmouth?
I went on the PoB in 2005, so I am definitely going to have to do a trip before the ship leaves service in September.