Sound systems: as I said in my original post, I'm sure many London sound systems are of good quality. The problem is the arrangement of the speakers, and it's no good relying on two speakers at one end of a hall. The volume has to be turned up to reach and to overcome the inevitable loss of sound, and then people who aren't dancing start shouting at each other to make themselves heard. I take Chris, UK's point about the limitation of house systems, but streamed audio is now possible, and I look forward to the day when neat, efficient speaker systems deliver adequate sound all over the dance floor, preferably without wiring. I agree with Charles Long that good quality sound is really important. If sound is well-focused it can change the dynamic of a milonga.
Several people have agreed that less teaching is good. My feeling is that London tango could do with many more practicas, guided or otherwise. After all, even in 21st century London, men can't dance on street corners with other men, and won't be able to until tango is vastly more widely known and accepted. We all need more secluded places to practice in. Then it should be possible for the dancers to invite in teachers to help and comment, rather than teachers running classes. Then dancers engaged in dancing would call the shots.
& Jantango tells me that Maipu 444 has closed. The upstairs room that housed seven milongas a week has been sold, along with the parquet floor that has welcomed the soles of many great names of tango. It's like losing a friend, even though I can't claim to be at all well acquainted with the place. No more videos on the Cachirulo YouTube channel with the familiar red and black tablecloths! Or maybe the tableclothes will move to Villa Malcolm, where the Saturday night Cachirulo Milonga will relocate, along with the house video camera.
PS: Melina has left a long and very interesting comment here as a reply to what Chris, UK said. There was a problem of emphasis in the translation, and she clarifies the kind of help she and Detlef try to give, to enable people to dance more easily together.