Another Brit here, yes cops do get punished in high profile cases with video evidence such as this.
The contradictory examples listed above were quite complex cases from what I remember.
That said, as a teenager a friend of mine was beaten up in a police van in a case of mistaken identity. He was advised by his lawyer to drop the case as there was little chance of proving what happened as the police had smashed up his phone which he had been recording them with.
Due to the context of police officers being injured prior to what’s shown on tape. I expect in this instance, the cop to get a lenient pushiment.