I think that before any extensive answer can be offered, we would need to establish precisely what part of the eighteenth century you are wanting to examine. A hundred years is a long time, and as u/Bodark43 alludes to, the perceptions of Scots Gaels by the general populace of London through that particular period of history were not static. Rather, those feelings likely would have largely aligned with what was being reported by the press, and would be further influenced by discussions in public spaces, whether that be workplaces or coffeehouses. Newspapers and magazines had various critical slants and agendas, of course, but for most of the century Scotland was very much a part of Britain, even if it tended to be considered 'North Britain' by a significant percentage of the London populace.

By 'common folk' I assume you are identifying a general snapshot of Londoners rather than specifically referring to the lower and middling classes who resided in the city. Still, greater degrees of leisure time and literacy for those more well-to-do could have some correlation with how information was disseminated and consumed, as well as how it was interpreted.

There is plenty of Scottish and British history to consider outwith the Jacobite risings, but in the eighteenth century English perceptions of the Scottish Highlands were strongly influenced by the fortunes of the British government's success in addressing the looming threat of a Scots-led Jacobite invasion, aided by the generational menace of France vis-à-vis the Auld Alliance. Fearmongering south of the border was rampant through much of the early century, and anti-Jacobite propaganda was promulgated by Whig institutions, citing recurring thematic bugbears like totalitarian monarchy and the corruption of bishops in Catholic and Episcopal church hierarchies. Scotland was hardly sympathetic to Jacobitism in a national sense, but the link between what was perceived as an atavistic, intransigent Highland culture and repeated attempts to overthrow the Hanoverian government and repeal the Treaty and Act Union of 1707 would grow to be indelibly cemented. This link was forged both by Hanoverian propaganda and indeed by the Jacobite army itself in 1745-6, when deliberate measures were taken by Jacobite commanders to unify a diverse host into a cohesive shock force, seizing upon the public's heightened fear of 'barbaric' Gaels through use of traditional Highland trappings like tartan and the wielding of pipes in war. This is significant to your scenario because Highland dress wasn't always necessarily equated with Stuart support, but there is something to be said about the perception of it eventually moving toward that equivalence in some circles – both in Scotland and in England.

Because Scotland had been regnally joined with England since 1603 and parliamentarily joined from 1707, by the last Jacobite rising in 1745 it had been intrinsically connected to the British polity for at the very least a full generation. With the ensuing cross-border political, economic, and social relationships, Londoners would have had plenty of exposure to Highland Scots through the entirety of the eighteenth century. Scottish-owned businesses would not have been uncommon, and prominent Scots flourished in banking, manufacturing, and trading. Whitehall was teeming with Scottish peers and some Highland gentry who conducted most of their dealings far from their northern homes. In their absences, they appointed factors to cover their estate business but remained directly involved through regular correspondence. Beyond this, consider that London was a thriving metropolis by the dawn of the eighteenth century, so not only would the presence of Scottish Gaels have been common, Scots ex-pat communities and even pro-Jacobite clubs and societies – composed of English, Scots, and many other nationalities – were both visible and clandestine across the city. There was plenty of room for different opinions in eighteenth-century London, just as any city today hosts a diverse array of cultures, communities, and faiths. In this sense, walking down the street in Highland garb probably wouldn't have mattered much to most people during most of the 1700s.

After the final defeat of martial Jacobitism at Culloden, the abolishment of heritable jurisdictions and collective Acts of Proscriptions in August 1746 (not in 1747 like so many have written) were implemented to hamstring the repeated recalcitrance of Highland communities that proved difficult to control. These acts largely targeted the Scottish Highlands both with intent and enforcement, even though the bulk of Jacobite martial support in 1745-6 was drawn from areas distinctly outwith the Highlands. Other legislation sought to disperse Catholic and non-juring Episcopal congregations, and some of these acts had already been implemented for years by the launch of the Forty-five. The Dress Act, the component of proscriptive laws upon which you comment, has arguably long been misinterpreted by modern historians and relatively little evidence has been found to show that it was strongly or commonly enforced. At most, I have heard of maybe a half-dozen accounts that were carried out on the local level by British army troops or Scots officials seeking to curtail treasonous behavior under their purviews. It appears that by 1760 the dress proscriptions were largely forgotten, though the act was not officially repealed until 1782. This appears to leverage almost half a century of popular indifference to the specter of Highland dress as a threat to civilized society, rendering a casual stroll in London likely a non-event.

The single best resource to follow up on the shape and depth of Jacobitism in London (and elsewhere in England) is Paul Monod's masterful Jacobitism and the English People, 1688-1788 (Cambridge, 1989). Other pieces by Nicholas Rogers, for example, could also be helpful. Of these, 'Riot and Popular Jacobitism in Early Hanoverian England' in Eveline Cruickshanks, ed., Ideology and Conspiracy: Aspects of Jacobitism 1689-1759 (Edinburgh, 1982), pp. 70-88, is likely the most relevant to your particular question. Hoping this has been of some help!

With best wishes,

Dr Darren S. Layne
Creator and Curator, The Jacobite Database of 1745

The costume laws changed. For about 35 years, after it was proscribed in 1746, what we'd think of now as Highland dress ( that had not had a very long tradition, it seems) was banned. Before then, it wasn't. That ban did not apply to the Highland regiments, like the Black Watch. It seems to have been a pretty effective ban there- few daring to wear kilts or belted plaid outside their homes. After James MacPherson kicked off what would be a Highland fad with his invention and publication of Ossian , in 1765, there would be greater use of Highland dress. That would increase enormously with the publication of Walter Scott's Waverly novels, which would result in quite an industry of creating Highland traditions after 1820, inventing clan tartans, increasing lengths of beards, etc.

Your essential question , though, is when and if you would be regarded as a Jacobite if you wore Highland dress. The history of the Jacobites is quite complex, and I don't really know it. u/FunkyPlaid has posted very intelligently on the subject, and with a bit of luck he'll wander over to say something.