...in that you can go to prison for expressing support for proscribed terrorist organisations as determined in UK law, and "Palestine Action" recently became one of them. For the avoidance of doubt, I tell you this purely for information and warning purposes only, and to help you, if you're British, avoid ending up in prison for expressing support for the proscribed organisation "Palestine Action".

Also to be clear: personally, I don't know much about that organisation beyond what's clear from their name and that they recently became proscribed.

Don't for a minute think that that doesn't include anonymously online. It absolutely does include what you write on the internet. It also includes (with lesser sentences) wearing clothing that supports a proscribed organisation or posting a picture of such clothing online or in print.

Historically there never was a right to free speech in the UK, although that changed somewhat with the introduction of the European Convention on Human Rights (which we helped draft post war and which has been extended since), but it is definitely illegal in the UK to express support in any way, including online, for proscribed terrorist organisations.

You can read more about the 84 proscribed organisations and sentences of up to 14 years in prison here: https://www.gov.uk/government/publications/proscribed-terror-groups-or-organisations--2/proscribed-terrorist-groups-or-organisations-accessible-version

The list includes organisations assessed by the UK government as terrorists, such as a lot of Islamist organisations, some far right groups and a handful of separatist movements.

Offenses include being reckless as to whether you might encourage others to support a proscribed organisation. So be careful about what you say and how you say it. Consider carefully whether you might encourage support for a proscribed organisation and don't do that.