I imagine the ridiculous scenes from the weekend, with hoardes of people behaving like it was a bank holiday, have forced his hand. Because of the blatant disregard of the advice to socially distance, it can pretty well be guaranteed that in two weeks' time there will be a massive spike in Covid-19 cases.
He tried to treat the public like grown ups, and explained why they had to socially distance/isolate, and it has been proved that the public just didn't listen or didn't understand (I suspect it's just the former)
I thought he looked not only exhausted tonight, but thoroughly pi**ed off - having to do this, probably ahead of the time they had planned for it.
My prediction is the army to be brought in to support the police, who will be overwhelmed by still having to deal with those who of course think that these rules don't, somehow, apply to them.
p.s. - Regarding the awful situation in Hitchin earlier - did you see that it was Tommy Robinson who came to the couple's aid. I saw a video posted (by him) and somehow he managed to make it all about him!