For mathematics, all the top-tier UK universities expect you to do a one-year taught masters (i.e. not a research masters) before starting a PhD. This certainly

For mathematics, all the top-tier UK universities expect you to do a one-year taught masters (i.e. not a research masters) before starting a PhD. This certainly includes Cambridge, Oxford, Warwick, Imperial, UCL and KCL. Cambridge calls its masters a "Part III" or "Certificate of Advance Studies" but it's definitely just a regular masters, albeit a really hard one. Mathematics PhDs in most of these institutions have a sort of informal target length of three years but usually take four years in practice. Funding is usually three years but often four, and the fees are often a tiny fraction of the usual amount in the final year to reflect that there is often a difference. I have much less knowledge of other subjects, but from the little I've heard the same seems to be true of chemistry and computer science. In short: I agree with the parent comment, at least for mathematics (and probably for all STEM subjects).