I never really understood why they didn't just have the first three bullets in a clip as rubber, unless they knew they where going against armored people, in which case SWAT would probably be called anyway.
I'm not aware of a less-than-lethal round you can chamber in a regular sidearm without sacrificing pretty much all stopping power. The first priority of a police gun is that whoever you shoot stops moving. There aren't really full power rubber bullets you can load into a gun and have them equally or even nearly as effective at that job as regular rounds. Rubber bullets for crowd control tend to come out of shotgun sized weapons, not 9mm sidearms.
As for British police overreach, excepting about three or four unjustified or questionable shootings by specialist firearms police (going back to 2005 here), there have been a couple of cases I can think of in recent years.
The first is the weird case of
Ian Tomlinson, a man who was pushed over and died during the G20 protests. The officer who pushed him, Simon Harwood, was found not guilty of manslaughter, despite the death being separately ruled unlawful and the officer's behaviour being ruled gross misconduct.
The other, which was viewed as a case of bad optics rather than misconduct or overreach, was the use of
mounted police charges as crowd control during the tuition fee protests in 2010 (
ground view). Horse charges are seen as a pretty major and violent tool, even if no harm is done. The idea of using those - combined with the heavy handed kettling techniques - against broadly peaceful and calm student protesters pushed the Met to further reform their riot control tactics, resulting in the oddly sensible hands-off approach to the later actual London riots. Then that approach got heavily criticised.
Oh, those riots were partially in response to one of those questionable shootings, but nevermind that.
There have been others, obviously, but those are the highest profile cases where there has been video and widespread attention. I'd note that the UK has far more restrictive laws regarding such video of, say, active court cases, so anything that is currently being prosecuted wouldn't be have any video or other information released until after a verdict to avoid potential prejudice of a jury hearing such a case. Even if such information leaked, publishing or spreading it could be considered contempt of court and be punishable with potential jail time. This has the odd effect of making more marginal but visible cases of misconduct better known than blatant and prosecuted cases, at least before conviction.