Just as free trade in terms of physical and intellectual goods makes us better off, so are we better off when human capital can freely cross our borders such that we can all become even more specialized in our work.
"The new wave of organised wildlife trade crime with heavily armed groups of poachers acting cross-borders is jeopardising conservation successes we've had in the past, " he said.
But Deputy Prime Minister Nick Clegg, whose Liberal Democrats oppose a referendum, said leaving altogether would "make us less safe because we co-operate in the European Union to go after criminal gangs that crossborders".