In UK, is the advertised salary range before or after tax?
Yes. Internal "grades" usually don't transfer between institutions.
I have just compared my (Russell Group, UK) university pay scale against the UCU one you link to and it is identical. That scale is gross, before tax, pay. I would expect net, take-home, pay to be about 30% less (after PAYE tax, National Insurance, and pension).


It is usual that the best I would expect you to be able to negotiate is one or two points on the spine system, in my experience.