Ofcom and Clearcast are tasked with enforcing the UK Broadcast Advertising Code (BCAP Code). Which came about from the Communications Act of 2003.
It is 100% government mandated censorship.
It is 100% government mandated censorship.
It appears to be established in law that Clearcast is an assistance service, and approval doesn't seem to be sufficient or necessary by law to ensure advertising is legal. It establishes risk, rather than making a legal finding.
If Mullvad's ad was 'banned' by Clearcast, what happened is that their ad didn't meet the standards that the industry has set for itself and the broadcasters didn't want to touch it.
(edit - does this make it 'better'? I don't know. It seems to me a bit like the situation in the US with HOAs, which heavily restrict what you can and can't do with your property, but aren't exactly government either. But I favour accuracy over emotion when talking about this stuff, which is why I wanted to point out the actual structure of the system here.)
Not remotely the same as a cabal of media conglomerates getting together to agree on their own rules about how they are going to interpret and enforce government-mandated censorship in society.
Not allowing advertisers to lie to advertise their product is I think not a kind of "censorship" one really needs to be worried about. They're free to advertise their product otherwise, they're just not free to lie to do it.
I feel silly making this elementary point, but freedoms can't ever be absolute in a society of more than one humans. Even in the US I bet you're free to drive, but you're not free to drive drunk. You're free to have sexual relations, but not with a minor. You're free to walk anywhere you like but not in other peoples' property and not on the streets with the cars (which btw is perfectly fine in Europe and it's rules about jaywalking that are "pants on head" for us).
These are rules. Societies have rules. They should have them. There's no problem with that.
And now my 16-year old self is very disappointed that I've grown up to be a conservative, establishmentarian fossil.
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[1] Coincidence. We're not all called something-akis.