Neither of those is nineteenth century
If the 'nineteenth century' thing isn't ironclad,.... And then there's also the aforementioned Home Rule civil war.
Home Rule and the Curragh is definitely the first choice. Cite
Hobsbawm as your authority for 1914 being 19th century. Home Rule is introduced, the situation gets worse, the army is actually in revolt, then war breaks out across the Channel. Instead of going to biff the Boche, the Army is used to bring about the quick death of Liberal England. Defence of the Realm Act remains in place.
As a Canadian in British politics, Bonar Law was clearly destined to be a dictator - like Napoleon, Stalin and Hitler, who were all from ethnic minorities/non-metropolitan territories. Sir Edward Carson would also fit that bill.
If it's really got to be 1800-1900, you could posit that Gladstone somehow gets the First Home Rule Bill through and the Curragh happens earlier. Maybe the Liberal Unionists agree to abstain because the Lords will block it, but he's got a secret deal to create new peers, or a terrible outbreak of Legionnaires' diseases at Westminster makes enough Tory peerages extinct for him his majority.... That's going to be an awful lot of fetid ermine though.
Earlier, what if Spencer Perceval had been killed by a French agent rather than a nutter? Panic amongst the élite, Army called out, Duke of Wellington takes over.....?