They gave up and retired when their savings or net worth, or something, reached £1m. I may have missed whether that included their house, which is pretty important..
Even if it didn't, I would say that £1m at 35-40, isn't going to be enough, £1m pension pot at 65 would give you 50k ish a year, 3% incrementing, before tax. There aren't figures from 40, but - maybe half? You'd be relying on stock market gains keeping you afloat, I think. But you might be unlucky.
That would be mbk's
high risk investment strategy to support
Picking the better sectors - not even the best - would have done it, in the last 20 years.
Keep payng NI at a low cost self-employed rate, to keep your pension!
Trouble is, when fit and 40 you can spend quite fast. I've met people doing constant travelling. You're likely to become cheaper to run when you're older!