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The box between the plug and the car generates a signal telling the car how much current the charger can pull. It makes this number up out of thin air. Usually it's pre-set to match the kind of plug the box was supplied with, but many of them are adjustable.
Double sockets are rated to 20A max and non-ring main sockets are often on 20A breakers. To go over 20A you'd really want to plug into two separate circuits, but if they're on separate RCDs one of those will trip because the neutrals will be unbalanced.
22 kW AC chargers require three phase, which you won't find in a UK home.
If you are talking AC charging isn’t the limiting factor the AC/DC converter in the car?