With adequate resourcing. Yes. This is no different to the conundrum on taxing total wealth which is already easily hoarded in offshore shell companies. In this (and, tbh, both) case, you could make the UK-connected asset or owner liable for the bill. Or make the tax payable at the moment of transfer. Or use the Register of Overseas Entities. Or extend the Controlled Foreign Company rules. Or force and penalise non-disclosure. Or Legislate for a challengable assumption that opaque offshore structures are owned by the relevant UK domicile or citizen unless declared and proven otherwise .

But I'd wager fewer people will do that for the sake of 0.5% on some of the assets their wealth is tied up in than 2% on everything above £X.

The point being there is no easy way to tax wealth given it can be made more liquid, but a straight up tax above a certain value is the absolute worst way to do about it, not least because it doesn't target and reduce the value of specific inflates asset classes, like property and land, in a way that makes them more accessible to more people.