Leaving the EU but staying in the single market would be the worst of all worlds - see my blog for the HuffPost

The pro-customs union/single market case is built on the false premise that a country’s prosperity is dependent upon the elimination of customs frontiers with countries with whom it conducts its trade.  However, this is far from the most important factor.  It is also not necessary to be a very large country, or part of a large trade bloc, in order to be prosperous.

Read more here.