Obviously there are individual cases that will be different (extremely high earners), but to support the market wide increase in property prices over so many decades now, there can only be structural explanations.
Low interest rates have played their part over the last 15 years, but the trend goes back further and the scale is bigger.
Housebuilding is another factor. The kind of house you're talking about, nice four bedroom detached, nice size garden, nice location, probably build 70-100 years ago, etc is very very desirable. Those kinds of houses aren't being build in great numbers these days. Not with the gardens, not in great locations, and obviously with period features.
We're trying to build cheaper "affordable" housing, different styles, new locations, smaller gardens. For anyone looking to buy or upgrade into the £500-£1m bracket there just isn't enough property to meet demand and prices have gone crazy. There are some £750k-£1m new builds but they'll have small gardens, and not be in the best locations, so people will pay more for a 30's semi in a nice established neighborhood with 100ft of garden.
But the big one, passing down significant sums from generation to generation is more or less a requirement in many parts of the country these days. Grandparents bought houses in the 40's/50's/60's, lived modest lifestyles and those houses are worth a lot of money. Parents bought houses in the 70's/80's/90's, have inherited wealth on top and are able to hand down large deposit contributions whilst they're still alive.
Whatever the rights and wrongs of the system are, if your family is NOT playing this game, then then you and/or your children are going to find it increasingly more difficult. Because other families are.