Yeah, it's a stupid situation. There's a property transaction tax, "stamp duty", which can be surprisingly high ( http://www.knightfrank.co.uk/stamp-duty-calculator ) but of course that really ends up protecting incumbents rather than taxing them.

Why would you want to tax sales of property? That just makes the market more illiquid, as well as making it more expensive to increase density (because you now to pay an extra a fee if you want to buy a single family house to replace with an taller building).

Yes, it's a bad idea. It used to be a small tax on high-value transactions only, but just recently it has been greatly increased.

The UK could do with a proper property tax, but since homeownership is the national religion that's not going to happen.