Very true.
Only new builds will have the amperage wiring. I think the current 'boards fuse' is 60A and some fast chargers are 48A. Under the max but still a lot of heat may be generated, but I'm no expert.
I'd be quite happy with a 13A granny charger, assuming I get another car when they are only electric.
Bit of a long story but we had our electrics assessed for a smart meter recently. A lot of work needed, some at my expense (ie removal of kitchen cabinet OR digging up a brand new drive). We didn't go ahead but it seems to get our house ready for a charge point might be £2000 to £3000.
Discussing this with a friend of a friend. This chap worked for Bentley on energy issues and also served on a committee advising government - he is a physicist by training. I asked him about the scare stories around granny cables and he said that that was exactly what they were, scare stories. Issues have arisen when people have used extension leads and not unravelled them (the heat builds up and can be a fire hazard) but he said you can purchase heavy duty leads and, if unravelled, they were fine. Granny cables themselves have a mechanism which causes them to trip out if they get too hot. He then said he used a granny cable himself despite having a charge point. He said they did a low mileage and a couple of trickle charges a week were adequate and better for the battery.
My son-in-law, a qualified electrician, also said that a granny cable was fine if used correctly. He recommended having a spur off one of the 13 amp plugs at the front of the house and getting a waterproof power point (commando?). He had earlier told me that the cable run from our consumer unit was not ideal.
So granny cables are fine, safe and ideal for low mileage users. The problem around terraced houses and apartments is a different matter altogether.