I've never had any trouble going anywhere on a ferry (with family, and activities week to france) and they did nothing, just let us drive straight on.. also at a service station (Oxford, the best services, EVER) me and 3 mates went up over a hill, sat near the motorway for 20 minutes, we smoked a spliff i rolled and a cigar i bought from the service station (70p hamlet lol). It made for a fun trip to france.
On the ferry on the way there, there was some guy cleaning the deck, so my mate decided to spit over the side (huge greeny) and it blew back and hit the cleaner's leg, it was great! lol.. Also bought a box of 10 cigars from paris and smoked them on the ferry