I think I can answer this pretty well. I've asked these same questions on this sub or the "parent" sub over a few years and it's always the same answer, an MSc isn't worth it at all because usually it's done to get into a specialized area or to just continue in Academia.

Getting a BSc in CS and then going for a MSc in CS again makes 0 sense as you'll go through the introductory stuff you did in year 1 and then you'll have optional modules and a project which is the same as year 3 of your BSc (depends what uni you're at)

Also let's say you study something like CS with the focus in robotics, machine learning or AI, a lot of the jobs for those area's don't require you to have the MSc at all, just your interest in the field and the prerequisite of a CS or Computing related degree.

The Big companies both tech and finance in London do favour top universities though, and that's a fact but you still have to have the proof to show for it, internships and good projects especially if you're trying to get onto their grad schemes or simply get hired.

If you've got good projects and some experience I don't see why you can't get £30k+ in London as a start (IMO) I'm going into my last year and I'd take the advice that user Opusly gave in the comments