With regards to the Coronavirus Lockdown rules, if you believe you have witnessed anyone or groups of people being non-compliant, the advice from Thames Valley Police is to call 101 and report it.
As a reminder, this is taken from the Government website.
Coronavirus (Covid-19): what you need to do.
Stay at home. Only go outside for food, health reasons or work (but only if you cannot work from home).
Stay 2 meters (6ft) away from other people.
Wash your hands as soon as you get home. You can spread the virus even if you don’t have symptoms.
It does go on to say, you can go for a walk or exercise outdoors if you stay more than 2 meters from others.