Had a chat with a friend last night who works in town planning at City Hall. She mentioned she published a report 2 years ago on pretty much what we're complaining about, which I didn't know. It was about change of use of existing units and the potential for more overall control local government and councils could enforce to maintain the character of a high street and mix of independent vs. multiples/chain outlets.
Once apparently discussed for about 3 minutes in the Assembly's Planning and Housing Committee, and then disappeared in a drawer somewhere with only a few councils implementing some of the advice.
Assuming that it wasn't due to the quality of her output, there is clearly little interest on some sides. Have asked her to send me a copy of the report, if anyone is interested, pls pm me.