The average tube driver's pay is ~42,000 pounds. That converts to $56,000 a year. That's not a very high income. That's solidly lower middle class depending on where you're living and whether you're single or the primary wage earner for your family. London is one of the highest cost of living areas in the world.

A family living in London with that income -- even if the second parent is also working -- is unlikely to have any savings. Unless the second family member has a high income information, tech, or finance job.