Scientists at Porton Down researched comical non-lethal crowd control devices

Instant banana skins, flying remote control planes into protectors to knock them down, knock out drugs and other things were proposed (and tested?)

According to recently declassified files from the National Archives, the military wanted weapons that would "incapacitate" demonstrators, allowing them to be captured. ...

The scientists were given the widest possible brief and came up with a range of weaponry that come straight out of the pages of science fiction novel.

They included a powerful, fast-setting, glue that when sprayed on clothes would instantly set them hard and so incapacitate the wearer and a super-slippery strip of road called an "instant banana skin" which would cause crowds to lose their footing.

The scientists also researched a drug which would safely knock someone out but they rejected the idea worried that anything made people unconscious very quickly risked killing them too. Instead, they worked on an "auto-inject dart" - to be fired from a gun - which contained either an emetic to make them sick or an anaesthetic to make them fall asleep.

However their favoured drugs turned out to be too dangerous. Files show the medical staff advised there was "an unacceptably high risk of death" with the vomit-inducing apomorphine.

The scientists seemed to do better with their "entangler grenade", another idea they took forward. This would explode in the air into coils of wire, landing on and immobilising protestors. The wire would be covered in fast-setting super adhesive and stick to rioters.

Royal Ordnance was asked to make up 1,000 of the grenades for testing but there the file ends - there is no indication of whether further tests were carried out. - telegraph

I once had a cool dream where rioters (not protesters, mind you, this crowd was rioting, not just exercising free speech. ) were made harmless by firing a bubble material at them. They were trying to fight but each person became encapsulated in his own bubble (not air tight). In my dream the angry people inside were still violently attempting to kill each other, but their bubbles were just bouncing around harmlessly. They could breathe fine and eventually, after they'd stopped struggling for three hours, the bubble would dissolve.