Of course, if they are caught they might not be meaningfully punished:
https://www.bbc.co.uk/news/uk-england-london-46370271
…and then there’s this, (I won’t say which frontline politician tweeted it):
“Knocking people off bikes is potentially very dangerous. It shouldn’t be legal for anyone. Police are not above the law”
They seems to acknowledge that the police aren’t acting illegally by saying it “shouldn’t” be legal. And then they say the Police are not above the Law, which suggests they do think it’s illegal. Possibly better to check before they commented.
*Not* knocking these guys off bikes is potentially more dangerous. They could kill themselves in a crash or spray acid in the face of a stranger. A bit of road rash is a small risk in comparison.