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Where i live in UK the market is pumped to the sky.

but how much could it really crash, down by half at best? not like a bitcoin crash, the land will always be worth something even if the bricks aren't.
50% crash is not probable. Although if UK was to leave the EU, that could lead to much less demand and in turn to properties prizes drop.
The good thing, if you're buying house (cash, not mortgage) for yourself (not to rent or re-sell), is that you don't have to be that much concerned about its value. All that really matters are your monthly costs, and the amount you save as compared to renting or paying mortgage.
As for land, you do have a point, but you don't know what the future will bring, the government can introduce tax on value of property (catastral tax), to prevent speculative land holdings and to generate more income.