The eschatological Protestant and classical republican contexts in which the ambassadors and the Rump placed the mission to the United Provinces makes it difficult to accept economic historians' explanation of the passage of the Navigation Act. Certainly it is hard to imagine that the calm, cool, and rational calculators of economic self-interest inhabited the same world as Walter Strickland, John Thurloe and Oliver St. John. Closer examination of the context of English politics in late 1651 makes it even harder to see the Navigation Act as the product of a group of merchant-interlopers.
The contemporary evidence which economic historians have adduced to demonstrate the political power of the colonial interlopers is of questionable quality. The material – a Royalist newsletter, the report of a Venetian ambassador based in Spain, and the account of the Dutch ambassadors to England in 1654 – all reflects the official Dutch and Royalist interpretation of English motivation. Not only does none of it come from sources who were in England in the summer and autumn of 1651, but it reflects the view of those who were unable and unwilling to understand the motivations for the English proposals to the Dutch in the spring of 1651. In fact, there is a good deal of evidence that the merchant-interlopers had little support in the government. The East India Company retained its control over exports of bullion. The Leveller William Walwyn's attempt to break the Levant Company's monopoly failed. The Greenland Company retained most of its exclusive rights.