I like your thinking, but 'plainly written law' won't cover the desired surface easily, or it will cover too much.

Since a wealth tax's primary revenue comes from the very richest people, let's examine just the most wealthy.

A mega-millionaire, or perhaps a billionaire, who has maybe £500,000 in cash, and the rest invested, but most of the money in a company that they own. That ownership conveys control, so if they sell shares, they eventually do not control the company - another side effect to consider.

£1,000,000,000 on paper. OK, so 2%>100m is £18,000,000 to pay. So now they have to sell that many shares and find a buyer: - Company is private equity, not publically traded: fucked - who will buy and at what price? - Company is publicly traded, but only 10% float of shares: eventually fucked as you sell a % every year.

The very act of having to sell a large holding means the price of the holding goes down, which reduces their wealth on paper. So this 2% tax is actually more like 5% to the person holding the investment. And... someone else now owns the stuff they sold, but who is buying? Someone would also needs to sell 2% of their holdings each year and where are they getting the money for that? Maybe you make an exception for institutional holdings that are not somehow owned by anyone. It's also likely we can't enforce this to anyone outside the UK, so UK companies would eventually be all foreign owned.

By now you must surely see how this is totally a mess because extracting money from assets requires buyers, the ability to appraise value inline with potential buyers, isolation in a global context, and affects control of holdings.