Re: Norway is in EFTA and Schengen...
Keep in mind that
* entering Norway you are only allowed to bring 5 liters of alcoholic beverages (less when hard liquors are involved)
* ...and 200 cigarettes (which costs around £100 in Norway)
So there is a huge incentive for normal citizens to become smugglers as they cross back into Norway. Unlike drugs, cheap beer is not frowned upon amongst the general populace. We all know someone who "takes a little extra".
But, Norway is only 5 million souls. Britain is slightly bigger. And who knows what EU will do with whatever border they share with Britain.