I would say Jake is from a very wealthy family! Also, his dad was as well — you need to read between the lines, as we don't like to acknowledge wealth and privilege in the UK.
A house that size in London would cost million(s), even some years back. Both Jake and his sister went to expensive private schools; this alone could set you back £100k or more a year. 99% people don't have this sort of spare cash sitting around! It's interesting the amount of
Jake's dad studied English Literature at Oxford. Along with the history of art and anthropology, this is a classic, soft, and private route into Oxbridge for those from a privileged private school background. It relies on social and cultural capital over pure intelligence.
All the evidence suggests Jake has significant, historical family wealth; the type that allows him to up sticks and "run to Japan" in his mid-20s. He's done really well, but whatever happens, he's not going to be destitute!