All separate breeds, all from Great Britain originally but developed from different bloodlines and/or counties. There are some distinct differences among the breeds when compared side-by-side, ie. Red Polls are always polled where the other two are not necessarily, etc. Look all three up on this website and this will help you understand the differences.
If you seen English South Devons they are nothing like a Red Poll or a Devon. They are bigger animals than the other two. They have lots more milk and generally are lighter in colour than the 2 other red breeds. They haven't entered into the "Black" types yet. Both Red Poll and Devon are great breeds in their own right and do well when crossed with others.