The film describes the French Revolution happening in 1771, and Napoleon being in power in 1784.
Britain was not at war when the story opens in 1770.
Jonathan Blake tells the young lady while sailing over to France, that Horatio Nelson had become Admiral of the Fleet. However, Horatio Nelson never was Admiral of the Fleet. In Horatio Nelson's career since joining the navy in 1770 until his death, the Admirals of the Fleet were Sir Edward Hawke, John Forbes, the Earl Howe and Sir Peter Parker. Nelson's highest rank was that of Vice Admiral of the White.
When Angerstein explains to young Blake the importance of British commerce, he conjures up English ships sailing to "...Hong Kong, Cape Town, Bombay...," he does this in the year 1770. Hong Kong was not an important port for British trade until it became a British colony in 1842, more than seventy years later.
Jonathan has an English accent as a child, yet he has an American accent as an adult.