In the UK an undergrad is 3 years in most cases, then 3 years for a PhD, so 6 years total.
Some institutions will technically admit you for a PhD with no prior degree at all, but nobody does this in practice.
Yes, but not a graduate degree.
For comparison, at least in Austria, you need to have finished both a Bachelor of Science (3 years) and a Master of Science (2 years) in order to be able to start a PhD.
That's usually not the case in the USA (and some common law countries), where you only need the equivalent of a Bachelor of Science in order to start the PhD. You then do a small version of the Master of Science in parallel with the PhD.
Tbh most Master’s, esp MSc, don’t add anything.