[Tim Skellett]

It's hugely increased and expedited trade within the EU; it's also played a huge role in making policies more consistant between its member countries, and it has successfully helped less developed EU nations to develop much faster.

It is often forgotten today how Britain begged to be allowed into the EU, and was rejected formally twice by de Gaulle; the trade advantages of being inside the EU are pretty damn big, and beat being outside of it hollow.