Just that technically where I live (in Zone 2 London) you need planning permission for AC with an outdoor unit. (Apparently it could be permitted development if they are for heat like a heat pump -- but not just for AC.)
I'm not willing to try my luck as I know my neighbors! But I haven't actually heard of anyone actually applying.
Thanks!
(Here's something I read about someone being forced to get planning after the fact. https://www.revk.uk/2018/07/air-conditioning-at-home-planning.html)