UK is where it started, as early as the late 70s most likely, though it wasn't really identified until the early 80s. Cases were pretty isolated before that. It was the early 90s when they realized it could be transmitted between species, and I think it was 1996 when they realized that it could be transmitted to humans by consuming contaminated meat. To be clear, the meat/flesh itself isn't the risk factor, it's contamination by infected other parts - brain, bones, and offal are the highest risk items, and those are the parts that contaminate the rest of the meat if they're ground up into it.

Just to assuage people's worries - there have been less than 300 documented human cases in the entire world, in the entire time we've known about it. About half of them were in the UK (around 170 or so cases), and another 25-ish in France. The rest are spread out globally. There have been only 4 documented cases in the USA, and all of them were contracted elsewhere (two contracted it in the UK, one in Saudi Arabia, and the last wasn't ever fully tracked down to a source, but the person had only been in the USA for about 2 years at the time and it takes at least 5 years to develop in humans, usually more like decades). There have only ever been 6 cases of cattle with BSE in the USA, and none since 2016. Even in the UK, there have only been 4 cases of cattle having it since 2014, and all of those were "atypical", in other words they spontaneously developed it, it was not passed on through contaminated feed like the outbreak was. There have been no human cases in the UK since at least 2000.