It isn't about the police having control of the street, TC. It's (supposed to be) about preventing the spread of the virus. People who are chucked onto the streets at 10pm on Saturday night will not go home to bed. It's also unlikely that they will hang about on the streets for the police to have any control over them (especially now it's getting colder). They will almost certainly make arrangements to head off elsewhere, probably to one of their houses. The "mingling" of people - which would be at least partly under control in a pub - will now be totally outside of anybody's control.
The problem is that the government believes that everybody will behave like good little children - and they won't. As I keep saying, people will socialise, they will mix and mingle and introducing a succession of arguably pointless rules will not alter that. Saying "the sooner everybody keeps away from everybody else the sooner we can return to normal" has been the problem right from the start. It is impossible to achieve that and the more it is tried, the more it will be ignored. Not even a complete lockdown will work. People still have to interact. Until that is accepted we will never return to normal.