Great post Jacippit..
If I was looking at having EV charge point installed I would definitely go down the Smart meter route. When arranging the smart meter install, if you mention EV or consumer unit upgrade and you require 25mm tails and Isolator then it will be done within the meter upgrade free of charge. If this isn’t arranged upfront though and the existing is 16mm cable then 16mm will stay in if the DNO fuse is less than 100Amp. They won’t fit an isolator either unless prearranged. Most fitters I’m sure will upgrade cable and fit isolator if asked nicely however a lot of this type of work is sub contracted out by suppliers and they might be paid price per fit so will do the bare minimum.
By the way if that’s your install then the cable to me looks like 16mm?