… if you already have a master’s degree, which takes 2 years. In the US many 5-6 year PhD programs do not require—and in fact include—a master’s degree.
That said, a masters degree in the UK is much less of an undertaking than many other countries. Level of independent research in my "combined" masters (4 yr course, usually taken as 1st degree), pales in comparison to what colleagues in mainland Europe had to do.
And it's possible to do a 180 ECTS masters (2 year full time) for four years part time.