For jobs, unless you're working in finance in London, for tech salaries (except for FAANG) it is simply no surprise that it is so low on average [0] that isn't even worth it.
What is more damning is that I saw an internship in the US earn more than a job posting of Head of Cyber Security at the HM Treasury which is $50-57K yr (senior level)
Doesn't matter if you went to the golden triangle of universities, it is much better to get a remote job in the US. each time.
As for startups, in the UK there is almost no connections here for VCs, angels or any investment network this might have changed in the few years but you would have to squint hard to find them.
[0] https://www.glassdoor.co.uk/Salaries/london-tech-salary-SRCH...