Just what exactly do our big firms get out of being in the EU other than the free trade deal? I'm sure there are numerous reasons but I don't have a clue. If we left then surely we would keep the free trade as with Norway?
There are harmonized standards, tariff free trade and a supply of workers to fill any skills shortage to name a few.
Norway may have full access to the internal EU market but not full access to all those the EU has done free trade deals with, only those that it has negotiated through the European Free Trade Association (in the main). Norway has to accept free movement of people and workers' rights, and potential future EU market rules, while having no say in what they are. It is also has to pay for this privilege and is the 10th largest contributor to the EU per capita. It also has significantly higher net migration levels than the UK.
Bear in mind the the Norwegians are actually very pro EU principles (they're even in the Shengen Group even though outside of the EU), but don't want to join the EU proper mainly because of fishing, farming and oil. What the people there would accept from a sharing of sovereignty point of view may completely different to what we would accept.