If you're concerned about a business or venue that's open and you don't think it should be, please check the guidance on this first.
https://www.met.police.uk/advice/advice-and-information/c19/coronavirus-covid-19/business-and-venue-closures/We're seeking to resolve situations where people appear to be or are contravening the government advice on physical social distancing and the stay at home measures without resorting to enforcement and issuing fines.
Please only tell us about something if you feel there is a significant issue or breach which you think we need to know about.
https://www.met.police.uk/tua/tell-us-about/c19/tell-us-about-possible-breach-coronavirus-measures/