My question concerns the television series "Poldark". The year of action in question is 1795, and Great Britain is at war with France. In spite of the state of war, a group of four Englishmen goes covertly into France to rescue a captured friend. The men sit in a tavern and mention to a French official that they are English, but "businessmen". This is accepted, although their presence is regarded as suspicious. Would the presence of Englishmen in such a situation have been possible?
This appears to be possible.
The first piece of evidence is "A Tale of Two Cities," which was set in France a few years before 1795, but during the French Revolution.
The second piece of evidence is the nature of the war itself. That is, France's main enemies were mainly Austria and Prussia (on land). The fight with England was mainly a sideshow. France and England were "barely" (not fully) at war. "Poldark" mentioned an English presence in Flanders (Belgium) which was Austrian territory, but whose coast England wanted to keep out of French hands. Unlike Austria and Prussia, England was waging a "preventive" war (mainly outside French territory), not an "invasive" war.
While France of the time was "suspicious" of almost everyone, her suspicions of England were far less than those of the Germans (Prussia and Austria), meaning Englishmen had some leeway. Until much later (Napoleon) England was not at the top of French worries.
The situation in Poldark is perfectly plausible in 1795, not just during the French Revolutionary Wars (1792 - 1802) but also during the Napoleonic Wars (1803 - 1815). This scenario would also work for French merchants in Britain.
Among Napoleon's thoughts while he was in exile on St. Helena was this on a comparison between the Law of Nations at sea and on land (he is referring to both the French Revolutionary Wars and the Napoleonic Wars):
...in a patent contradiction, a British vessel (in the event of a war between France and Britain) that is found in the port of Nantes—e.g. when war is declared— will be confiscated. The men on board will be prisoners of war, even if they are non-combatants and simple citizens. By contrast, a shop containing British goods belonging to Englishmen living in the same town will be neither sequestrated nor confiscated; and British merchants travelling in France will not be prisoners of war and will be afforded right of passage and the passports required to leave French territory.
Source: Napoleon: On War (edited by Bruno Colson, translated by Gregory Elliott)
Prior to the 1793 Alien Act, which became law less than a month before Britain and France went to war, there were few restrictions on foreigners entering the country. The 1793 Act meant, among other things, that
Foreigners were allowed to arrive only at certain ports and their movements from the port of arrival to their destination as well as in the country were subject to controls and restrictions. Only foreign overseas merchants were exempt from them: they were allowed to travel freely within the country.
It was not until 1798 that foreign merchants were subject to the same regulations as "other immigrants and foreign travellers".
Source: Margrit Schulte Beerbuhl, 'British Nationality Policy as a Counter-Revolutionary Strategy During the Napoleonic Wars' in 'Migration Control in the North Atlantic World' (Andreas Fahrmeir et al, eds.)