Switzerland and Norway are proof that you can do very well outside the EU.
In case people in Britian are worried about how life would look like after they leave the EU, all they need to do is to look at Norway and Switzerland. Both Switzerland and Norway, while being members of the "Schengen Area", never joined the EU (along with Iceland), and both countries are doing much better economically than most of the EU member states today.
According to the "The World Economic Forum" (WEF) The best performing economy in Europe is Switzerland, which isn't part of the EU. Switzerland, which takes pride in its neutrality and independence, voted decisively not to be part of the EU in 2001. Like Norwegians, who are also are not members of the EU, the Swiss have a high standard of living, with a per capita GDP of US$60,491. Nearly 77% of the Swiss voted not to open negotiations for membership in the EU. In 1992, the Swiss also rejected the option of joining the European Economic Area. The economic relationship between the country smack in the centre of Europe and the EU is defined in a raft of bilateral agreements which the Swiss can renounce at any given time, by a stroke of a pen.
Norway, with a population of 5 million, has held two referendums on joining the EU in 1972 and 1994, and on both occasions Norwegians voted "NO". While not part of the European Union, Norway is part of the European Economic Area. In this way, it has access to the European market but is not part of its political union. While Norway accepts some EU rules and regulation in order to obtain access to the EU's single market, Norway has the right, unlike all other EU members, to refuse to apply EU laws whenever it chooses to do so. While Norway makes financial contributions to the EU, it does so in order to insure access the the EU's single market and not as an EU member. This means that Norway, unlike members of the EU, retains its independence and sovereignty, and is not bound by any EU laws regarding foreign affairs, defence, immigration, criminal justice and domestic affairs. Also the best place to live in the world, according to the the United Nation's annual Human Development Report, is Norway, which as been noted before, is not a member of the EU.
If you have a strong economy, as the UK has, you could do much better outside the EU rather than inside it, as Norway and Switzerland have already proved, and the best part is that you won't even have to give up your sovereignty and independence to unelected bureaucrats in Brussels.