I have read the following (and similar) frequently – “Is charging your car from a domestic socket safe? While 3-pin plug sockets can charge EVs, they are not designed to support the kinds of loads for the time periods that EVs require. These loads can cause heating that tests the quality of historic domestic wiring, as well as the socket” Now the above may relate more to full EVs that take many more hours to charge than PHEVs, but I’d still get my wiring checked first. I guess Brydo had his checked when the outdoor socket was installed.
As a sparky by trade I couldn’t agree more @gliders. My advice would be if you have the old black style rubber sheathed twisted cable which only contained a 1mm2 earth or rewireable fuses on your consumer unit get it checked by a qualified spark regardless.
Newer PVC cables aren’t so bad even if the older red and black as long as you have a modern RCD/MCB consumer unit. Better still but not essential if its on its own circuit protected by a RCBO. That way if ever there was a fault it would not trip the rest of the house.