I like it and as long as it could be processed quick it could work. The main issue with it is processing stuff as i understand it. We often hear coppers say a simple stop and search can result in hours of paperwork. If fining for this issue was similar they would very very quickly bog themselves down with paperwork.
One other issue is proving certain situations were against the rules. Stopping someone on the street for example. They go to fine them and the person replies that it is the first time they have been out all day and it is to get essentials from the shop/checking on an elderly friend before bed etc. The police may even have had calls about this person but a concerned citizens comments are still only hear say as far as the law is concerned. They would need to sign written statements etc for it to be worth more. That it's self is an issue, all that hassle for one bloke who is going for to many walks. If you started taking statements and all that stuff then that is as good as 2 coppers full shift taken up with 1 single incident of which i assume there will be many.
I do like your idea but in practice i can see a load of issues, in fact it's pretty much impossible to police properly currently. I think only major incidents like a big party getting busted will get any real action taken against them. Even then what action? if people do a runner, will police see it serious enough to chase them down like a legit criminal? I can see it now, Dorris from number 34 with a police helicopter spot light pointing her out as she feeds the donkeys in the field across the road for the 3rd time in one day as a ground unit move in on her hehe. Okay that is just a funny idea but you see where i am coming from. What resources to use, how much force in some situations is merited etc.
Unless it is some sort of total lockdown the police are being put in an impossible situation as i see it.