One: early retirement
Two: the idea that the recruiter was right about not being able to find the money elsewhere
You have a PhD in Computer Science, one of the highest academic accomplishments in one of the hottest fields for the last 30-40 years. I want you to know how far ahead you are of people like me who just taught themselves to code and glue web apps together for 6 figures. You need to dispel the notion that you can't find your current salary elsewhere and that recruiter was likely lying to you. Finding meaningful work is a different beast, but you're staying attached to a job for a financial goal that isn't really clear.
Assuming you stayed at this job, how long until early retirement? It might make more sense to enjoy things now and take a break from working, move to a new city with a lower CoL (plus you don't even like London), and try a better work/life balance.
Depending on your flat's rent and joint savings, it might actually make more sense to leave the flat, put that money towards traveling (which probably won't even come close your rent), and figure things out. It's not like you're building capital renting the place anyway.
As a final bit, career suicide is a dead concept in CS. That seems like extremely outdated thinking especially with remote work's popularity now.