This is much harder to evade - if you own most of Mayfair, you can't just move your assets elsewhere - they are very clearly tied to the location.
Of course, this would mean taxing powerful aristocrats, including the royal family. With their large majority, the British government had the opportunity to do this, but decided to take an easier path. The reason why this path was easier is now becoming clear to them.
It's a loophole the mega-rich are using to avoid tax.
The other thing that's happened is that a lot of the mega-rich have lobbied to gradually chip away at inheritance taxes. So again they just pass the asset, paying a fraction of the taxes they'd have paid had they been a "normal" tax payer.
And one of the big things they've got? No capital gains on those stocks when passed to children.
So yeah, we need to tax assets as well as income. Because anything that's not taxed the rich just funnel money into it to avoid paying tax.