[4] It was not till 1696, however, that this Board became permanent. More important, they worked out a new colonial policy, which was to remain, in its main features, the accepted British policy down to the loss of the American colonies in 1782. The theory at the base of this policy was that while the mother-country must be responsible for the defence of all the scattered settlements, which in their weakness were exposed to attack from many sides, in she might reasonably expect to be put in possession of definite trade advantages. Hence the Navigation Act of 1660 provided not only that inter-imperial trade should be carried in English or colonial vessels, but that certain 'enumerated articles,' including some of the most important colonial products, should be sent only to England, so that English merchants should have the profits of selling them to other countries, and the English government the proceeds of duties upon them; and another Act provided that imports to the colonies should only come from, or through, England. In other words, England was to be the commercial entrepot of the whole empire; and the regulation of imperial trade as a whole was to belong to the English government and parliament. To the English government also must necessarily fall the conduct of the relations of the empire as a whole with other powers. This commercial system was not, however, purely one-sided. If the colonies were to send their chief products only to England, they were at the same time to have a monopoly, or a marked advantage, in English markets. Tobacco-growing had been for a time a promising industry in England; it was prohibited in order that it might not compete with the colonial product; and differential duties were levied on the competing products of other countries and their colonies. In short, the new policy was one of Imperial Preference; it aimed at turning the empire into an economic unit, of which England should be the administrative and distributing centre. So far the English policy did not differ in kind from the contemporary colonial policy of other countries, though it left to the colonies a greater freedom of trade (for example, in the 'non-enumerated articles') than was ever allowed by Spain or France, or by the two great trading companies which controlled the foreign possessions of Holland.