Well there's two at the moment, the Proffessional Standards lot which basically means the old bill investigate themselves or there's the IOPC who are independent of plod and investigate without prejudice.
In this case though, matey had broken the law and was rightly found guilty.
Personally I think "losing" body cam footage should at least be a punishable offence and at worst be a case of perjury. Easy for me to say yes as I'm not plod but I think what needs to be hammered home, not just to UK cops but to EVERYONE who wants to be a copper is that they should realise they are held to a higher standard than everyone else. Far too many people join the police for the power trip, the pension or the machismo which are exactly the reasons they should be barred from becoming cops. Good cops know the law, know right from wrong and hold themselves to a high standard before others. Sadly that can't be taught easily and it shows in modern policing, not just in the UK but in the USA and beyond.
I've always said (and still do) that the George Floyd case was a case of bad policing, not racism. If you look at the behaviour of a large proportion of the police in the USA you'll see that the training, the culture and the standard of individual policing needs a huge overhaul.