How exactly does that destabilize the currency or eliminate the right to private property? All countries that tax wealth or income reserve the right to investigate how much wealth and/or income you have and ask questions about where it came from, and reserve the right to punish you for not cooperating.

They also reserve the right to investigate crimes and compel cooperation with investigation.

From the primary source linked by that Wikipedia article:

A UWO requires a person who is reasonably suspected of involvement in, or of being connected to a person involved in, serious crime to explain the nature and extent of their interest in particular property, and to explain how the property was obtained, where there are reasonable grounds to suspect that the respondent’s known lawfully obtained income would be insufficient to allow the respondent to obtain the property.

So if you're a known associate of, say, a mobster, and your income tax documents say you made £100k last year, but you suddenly had £2m cash to spend on a choice piece of real estate with no record of you taking out a mortgage or other loans, yeah, they're going to want you to explain where that money came from, and the law gives them the option to compel you to do so. This is how the rule of law is actually supposed to work!

Wow, so much for "innocent until proven guilty".

I imagine it's like most money laundering laws where the circumstantial evidence that prompted the investigation is enough to convict if you don't provide a verifiable explanation.