Sure. OP never said anything about retirement. It’s definitely a substantial amount though.

That’s the median household income in the UK as of 2020, which is about half of what it is in the US, which is where I came up with my ratio.

900k pounds is a lot though. You can get by with much less in Europe. I would say this is already equivalent to 1.8M USD in terms of lifestyle.

OP’s customer probably thinks that’s a great idea!