The BBC Farming Today program had an interview with a farmer who owns a lot of farms in the UK and in Europe. He raised the point that if we leave the single market and go back to things as they were, it would take 3 sets of customs clearances to move something as innocuous as celery to or from Spain to the UK. All of which have to be filled in perfectly and have to be checked and processed.
I don't know the in's and out's of it, but my guess is you need paper work to export it from the UK, paper work to get it into and out of France and finally paper work to get it into Spain. And you may well need to pay taxes and import duty at some point.
With the single market you just arrange transportation. Duty and customs don't happen within the single market.
Of course Leavers will tell you that we'll negotiate access to the single market as part of our exit deal, but:
- There is no guarantee that the rest of the EU will give us access to the single market, and despite what the Leavers say about the EU needing us more than we need them, it is not guaranteed. Suppose they decided to shut us out just to spite us for leaving?
- If they do give us access you can be sure there will be a big price tag attached to it, either financially or by demanding we allow freedom of movement, or more likely, both.