Another possibility is that a lot of it is bought using borrowed money. Especially if much of your own money is in the stock market, it may be beneficial to take out a loan to buy something compared to selling other assets to raise the same amount of cash. Even going by the likely relatively conservative £200K/year before taxes, you are looking at a very nice house going for perhaps around 3-5 years' worth of pre-tax income.
Let's say you have good contacts at the bank and can secure a loan for £500K at 3.5% interest (not at all unreasonable if you make half that before taxes in a single year and purchase something that can be used as collateral for the money borrowed; with a bit of negotiating, I wouldn't be surprised if one could push the interest rate even lower, and stock in a publicly traded company can also trivially be used as collateral). That's less than £1500/month in interest, before any applicable tax effects -- less than 10% of the before-tax income. And like @Victor wrotelike @Victor wrote, I think it's reasonable to say that especially if the company is publicly traded, the CEO makes more than £200K/year. Given an income of £200K/year and assuming 30% taxes on that amount (the marginal tax would likely be higher, and this includes e.g. interest expense deductions), the money left over after taxes and interest payments on a £500K 3.5% debt is still about £10K/month. Even with a pretty rapid amortization schedule and even if the actual tax rate is higher, that leaves quite a bit of money to be socked away in savings and other investments.