[seanhunter]

You understand incorrectly. At least, fiduciary duty is absolutely not required to establish insider trading in the UK market abuse regime (or the EU which is similar). In the UK, simply trading on the basis of material non-public price-sensitive information is insider trading.

In the US there have been some cases which make it very hard to actually be convicted of insider trading in actual practise, but fiduciaries are not the only insiders in US securities law. Here's more details. https://www.investopedia.com/terms/i/insidertrading.asp