By the second of the rules annexed to the Act of Parliament which imposed what is now called the Old Subsidy, every merchant, whether English or alien, was allowed to draw back half that duty upon exportation; the English merchant, provided the exportation took place within twelve months; the alien, provided it took place within nine months.
As it is the interest of the freemen of a corporation to hinder the rest of the inhabitants from employing any workmen but themselves, so it is the interest of the merchants and manufacturers of every country to secure to themselves the monopoly of the home market. Hence in Great Britain, and in most other European countries, the extraordinary duties upon almost all goods imported by alien merchants.
A few selections from The Wealth of Nations (Chapters III, IV) by Adam Smith: