I am in England and have always been fascinated with your 'late unpleasantness.' I have an uncle, brother and cousin who share my interest and occasionally meet folk who are also interested. American history is very popular among undergraduates, certainly in the universities I have known, though the Civil War tends to be taught lately as part of courses centred on the wider African-American experience, US politics or military studies.
My personal introduction occurred about 1973 or '74 when my uncle gave me a copy of Bruce Catton's trilogy, having already taught me a few years earlier the words to 'John Brown's Body' and 'Tenting Tonight.' He taught literature at a public school (I think you would call it a private school) and he had a great love of Faulkner and Crane, too - which all seemed to tie in in the mind of a child. Aged 3 or 4, I thought it was all still going on! There was a collection of Civil War songs on record; the Folkways boxed set collected by Irwin Silber (if that is the correct name). Staying with my uncle was a delight: we would eat a supper of beans and sausages in the garden, drinking coffee (which we never did anywhere else - always tea) - and pretend to be Lee or Grant and staff-officers at a particular battle, deciding on the plan of action the next day. Looking back, it was all a little 'lost cause' tinged, as my uncle's sympathies were with the Confederacy purely on the basis that (from an English perspective) the 'states rights' principle had been established during the Revolution. We did discuss slavery occasionally ('To Kill A Mockingbird' was another of his favourites), but it was mainly the military side that interested his young nephews.
I think more generally, British people are aware of landmarks in American history to a wide extent, of which the Civil War is clearly central. Catton's works sold well over here as did McPherson's 'Battle Cry Of Freedom.' Popular media holds sway, of course, and the PBS series by Ken Burns reached a new audience here as I am sure it did in the US. I cannot be alone in much-admiring Shelby Foote on that basis, though not agreeing with some of his opinions. I think for the current generation of students, websites like Youtube do a grand job of making available lectures by such luminaries as McPherson, David Blight, Gary Gallagher Ed Ayres - so it is available to interested undergrads.
Apologies for rambling on. You ask a thought-provoking question.
Bringing the