After that you enter into the Ph.D. for 3 years(max 4) and you are right, you can almost do whatever you want. Just bear in mind that either you publish in top journals or your academic career ends here.
Then there's the program itself. DTCs (doctoral training centres) now mostly run 3 + 1 programmes, where your first year is a master's, involving taught classes and a research project. This is to get everyone up to speed on how to actually do independent research, and to build core skills. While it's true that teaching doesn't always form a mandatory part of a doctoral degree, working as a teaching assistant for at least one semester is often mandatory.
In short, you've mischaracterised doctoral education in England and Wales (Scotland may be different) to quite an extraordinary degree. I see no reason to comment upon the "more than our top share" claim, for reasons which are, I hope, obvious.
Well I'm not sure that many people without a first would seriously consider doing a PhD, so this isn't relevant in most cases.
> DTCs (doctoral training centres) now mostly run 3 + 1 programmes
Right, which is a big disadvantage of them. DTCs are just one way to do a PhD and they're not the traditional approach in the UK.
> In short, you've mischaracterised doctoral education in England and Wales
I don't agree! This matches from I see of students going into and coming out of the system today.