It should be, unless there is a legitimate reason for blocking it. Hefty fine.

I don't think it's legal to walk across or stand in the middle of the road to begin with (anywhere except a crosswalk while the light is red).. but besides that, no, I don't think there should be special laws against it, because I think a little bit of economy/commerce/workforce/car-pollution-jamming is a good thing. The protests behind those road blockages are probably more important than the ability of the drivers to get where they want to go, and making it illegal is just authoritarianistically preserving the status quo.

Chains & punishment? You name the time & place! 😈

Yes. I don't know, maybe a several hundred pounds fine that goes to a good cause.

critical mass babey!

Why should that be a crime?

Yes that's what we call in bird culture "a dick move". Should be some kind of traffic infraction that carries a serious fine because you can be ticketed for driving too slow on the highway or jaywalking.