The Wealth of Nations by Part 5 Chapter 2 Page 258

great consequence, takes place in all the different parts of the United Kingdom of Great Britain, leaves the interior commerce of the country, the inland and coasting trade, almost entirely free. The inland trade is almost perfectly free, and the greater part of goods may be carried from one end of the kingdom to the other without requiring any permit or let-pass, without being subject to question, visit, or examination from the revenue officers. There are a few exceptions, but they are such as can give no interruption to any important branch of the inland commerce of the country. Goods carried coastwise, indeed, require certificates or coast-cockets.

If you except coals, however, the rest are almost all duty-free. This freedom of interior commerce, the effect of the uniformity of the system of taxation, is perhaps one of