Hope it helps...

I think you would be better of reading the original paper on this topic published by the Home Office when you have more time on your hands.
According to my understanding, it is not an automatic qualifying process,not as you mentioned "也就是各种签证经过若干年合法居留之后，达到资格可以直接加入英籍".
The new legislation has divided potential candidates into many groups. Different groups have different qualifying criteria. Some easier and simplier thant the others.