Customs checks at Santander ferry port

depends if you are in car or van,  most cars just go through without being stopped.

Depends, you can be one of the thousands that don't get stopped or one of the few that do get stopped, it's a lottery! We've done the trip regularly and only been stopped once. Matters not being a resident or a third country national.

Do the Newhaven - Dieppe crossing. When you get to the customs checkpoint, tell them your not staying in France, your driving through to Spain. At that point they lose all interest and send you on you way. Done it twice in last couple of months and exactly the same each time. 

More interested in registering dog than checking goods

James

As the ferry comes from UK (a 3rd country), this week, seems to be different (after 30 years) There is a recent change towards the exit. .... the options ...go straight through and take a (high) risk of being stopped, choose pets lane, or items to declare lane. Point to note.... car deck has surveillance during crossing, and on leaving the ferry one can see security with lists of vehicle numbers and stopping vehicles before they go through entry point.