https://www.ofcom.org.uk/siteassets/resources/documents/onli...
It amounts to your basic terms of service. It means that you'll need to moderate your forums, and prove that you have a policy for moderation. (basically what all decent forums do anyway) The crucial thing is that you need to record that you've done it, and reassessed it. and prove "you understand the 17 priority areas"
Its similar for what a trustee of a small charity is supposed to do each year for its due diligence.
this is similar to running a cricket club, or scout club
For running a scout association each lesson could technically require an individual risk assessment for every piece of equipment, and lesson. The hall needs to be safe, and you need to prove that it's safe. Also GDPR, and safeguarding, background checks, money laundering.
> hold up to legal scrutiny from an activist court official
Its not the USA. activist court officials require a functioning court system. Plus common law has the concept of reasonable. A moderated forum will be of a much higher standard of moderation than facebook/twitter/tiktok.