I've worked for several years in the UK now, and from conversations I've had with UK academics (particularly philosophers), I found the following as a typical career trajectory for recent PhDs. I'm not saying this is the only path to a permanent job, but I've heard many UK lecturers describe this as how they got where they are.
You get funding for 3 years to do your PhD. There's no obligatory coursework (many PhD students start out with a 2-year MA which does have coursework, though). You are encouraged to teach a bit starting year 2, but your primary duty is writing the thesis. Most people do not succeed to do this in the three allotted years. and need to take at least one or two semesters more. They get by through teaching, other jobs (one person was a waiter) or cannibalising their savings. When you defend your PhD, you typically have 0, 1 or rarely, 2 or more publications.
Your next career move is a stipendiary lectureship (a bit like adjuncting in the US) where you’re paid a bit better than you were as a grad student and get more teaching experience. Still, it’s a lot of work for little pay and does not really allow you to do research as you would need to be competitive.
Then, after half a year or so stipendiary teaching, you land a postdoc.
Lecturers very rarely come directly from grad school and thus the level does not really correspond to that of an assistant professor in the US. At Oxford University, all lecturers are officially called "associate professor", for example. Also, there is no elaborate tenure process like in the US (with the exception of rare tenure track positions such as Chancellor's Fellowships in Edinburgh), but there is a trial period, anywhere between 6 months and 5 years.
Once you have a lectureship, you are relatively secure. The pay is OK but not great (compared to US positions in particular). You can get promotions within your university (next steps are senior lecturer, reader, professor - the reader level is phased out at some institutions).
Most people I know who get their first lectureship are in their early to mid thirties. If, after two or three temporary positions you do not secure a permanent position (so we are now speaking between 4 and 9 years post-PhD) things start to seriously weigh, the frequent relocation, relatively low pay, and continued insecurity in particular. Some people opt out of academia, others continue to try.
The quite long period on fixed-term positions (involving frequent relocations) is a recurring theme in the career trajectory of UK philosophers I have talked to. There are some exceptions. Some people land a prestigious Junior Research Fellowship (JRF, research-intensive postdoc) at Oxford or Cambridge right out of grad school and find a permanent post within three years. Very rarely, people get hired right out of grad school. Purely anecdotally, I found most of these to come either from Oxford or Cambridge.