Anti-social behaviour and street racing

Got a group of lads racing round the local area in high performance motors such as Merc AMG’s, Audi RS3’s and Range Rover SVR’s and so on. They’re racing each other at excessive speeds along narrow residential streets and busy main roads. It’s only a matter of time before someone runs out of talent and kills or seriously injures someone.

Question is do I ring 999 or 101? Is it a waste of time? If police respond what’s the likely outcome?

I have reg numbers and car descriptions. I’ve got videos of the cars pulled up revving engines loudly but nothing of them racing. They’re just going too fast for decent enough mobile phone video to be used as evidence.