Ah… English naming convention.
Streaky is what most Americans are referring to when they say bacon. That streaky looks like what would be higher end bacon in the US. The cheaper stuff is cut thinner and has more fat, though they always put the lean slices by the window…
Back bacon is a combination of what Americans call Canadian Bacon and Bacon. A bit of belly (the streaky portion and a bit of loin (the lean, round section). Hard to find here, as we butcher the animals in a different manner.
It’s all tasty. Should not be sour if cooked just with straight heat and it’s own rendered fat.