I have an Anglo-American TL that has this. POV is vaguely in 1774; the important consequence is that the Revolutionary War is forestalled (rather than defeated) and the colonists get representation in Parliament, which reformers like William Pitt use as a way of diluting the British rotten boroughs. The important aspects of this are,
- There is no Louisiana purchase. Louisiana is French, and has little white settlement north of OTL's state of Louisiana, except St. Louis. Britain notably chooses not to seize it at the end of the Napoleonic Wars. It buys off the northernmost parts later to facilitate transcontinental railroads, but that's not even all of OTL's Montana. In between OTL's Montana and Louisiana, indigenous people remain de facto (later de jure) independent. No slavery.
- Slavery gets abolished on the British schedule, i.e. in the 1830s. The American South is too weak to resist the combined powers of the American North and Britain proper. For the same reason, civil rights laws get enforced early - universal male vote happens on a compromise schedule between OTL's Britain and white America, in the 1860s. With no independent Supreme Court, a parliament dominated by the metropole and the American North can more easily pass laws limiting segregation. (But laws against job discrimination have to wait until OTL's schedule in the 1960s.)
- A generally stronger Britain in the mid-19c is in a stronger position to enforce the international ban on the slave trade, which leads to slightly faster abolition in Brazil than in OTL.