Since then I've built up a network of connections and beefed up my skillset (spending more time with js frameworks such as Angular) and since received offers in the £65-70k mark. These were always "senior tech lead" positions, but they never seemed like real management jobs and I'd still spend the majority of the time writing software.
In the end I've jumped to contracting because the money is 2-3 times that of permanent roles and it was just too tempting. But the roles are there, especially in London - Ruby devs included.
London is its own micro-world. In the same way SV != USA, London != UK. Perhaps moreso here, seeing as the country is smaller.
I would posit that you also have very good sales skills or are working in an in-demand niche (mobile?). I would've loved to be there after 2 years' experience; alas learning to big myself up took a bit longer!
After starting out doing Ruby on Rails, I moved to backend development focusing on Devops/PaaS — not super-niche but definitely more in-demand than Ruby on Rails, which that's one of the reasons I switched (as well as enjoying it more). Furthermore it's has the advantage of being a Hot New Thing™, which means you gain seniority much faster — in Ruby on Rails it might take 4-5 years to be considered 'senior'. In a much newer technology (like Angular for example), you might only need a year.
* Graduated in 2012 and took a job in the South East (not London) - £25,000
* Left after 18 months because high cost of living and salary increases were below inflation (small company with money problems). Moved to North West and took a job earning - £30,000
* Left that job and took a cut down to £27,000 because I wanted to work with rails and it's hard to find rails positions here in the North West
I could probably be earning more money but getting professional rails experience is higher on my list.
It's hard looking at US salaries and not seeing jobs offered anywhere near those rates here in the UK. I guess if you want to earn over £50k a year before you're 30 in the UK you have to be a contractor.