A fuse works by melting, so clearly it produces some heat, the problem with the 13 amp plug is changes from the original design with insulators on the live pins means it can't transfer the heat into the socket as easy any more, so at max rating over an extended time the plug can over heat, so the typical granny lead is 2 kW not 3 kW due to the extended time it is on charge for.
I don't have the latest edition of BS 7671 and I hear people say we should not use commando sockets with domestic, however nearly every caravan and boat are supplied by commando sockets, and they are domestic, so some thing does not ring true. The idea of a 32 amp commando socket seems good, as it can not only supply an EV but other items like welding sets, however the problem is the use of TN-C-S supplies, and the possibility of DC freezing a RCD.
So we need two protective devices, one is
loss of PEN detection, and disconnection and the other is 6 mA DC detection and disconnection, many of the leads incorporate the 6 mA DC detection, but the loss of PEN seems to be only included with fixed EV charging points.
Be it 2, 3, or 7 kW the loss of PEN is the big problem. The idea of the granny lead is for emergency charging when away from home, and it seems doing a risk assessment the chances of there being a loss of PEN at the same time as using the emergency charging lead are low, so some one it seems feels we can take a chance, and I have used class I items in my garden from time to time, like the standard car battery charger. Although the ones I have now are class II.
The other option is a TT supply, but banging in earth rods also comes with problems, not really a DIY job, the
IET supply to outbuildings does go into some of the problems. I have included links mainly to show how complex, rather than expecting you to DIY the work.
If the whole car, or caravan is inside a building which is itself bonded then the loss of PEN is not a problem, so using the granny leads in a garage is not a problem, so a 32 amp commando socket in the garage so both welders and car charging units can be plugged in makes sense, and maybe the granny lead is intended for use in a garage?
The use of type A rather than type AC RCD's is required, however any new installation today can't use type AC anyway, but the 6 mA is not much, and only EV charging leads seem to have DC detection, and other items also produce DC like the three port valve used with central heating, without looking at faults with LED lighting etc. I take the attitude which maybe wrong, that with 14 RCBO's (RCD and MCB combined) that the chances of earth leakage and DC injection at the same time on the same circuit is slim, and the RCD part of the trip is secondary protection anyway, so even with type AC RCBO's I am not really worried.
This is also a point with EV charging, if the charger is the only item supplied from that RCD then the chances of both DC leakage and an earth fault at the same time is slim, although not impossible, however you would not want the EV charger to be supplied by the same RCD as other items in the home, as it could be rendered inoperative, not only by the EV but also other items in the home. So the EV charging point needs its own dedicated RCD, so this rules out any idea of supplying it from the ring final.
If you consumer unit is using two RCD's feeding so many MCB's each, then by moving to RCBO's it also frees up 4 slots, so room for the dedicated supply to the EV charging point, and even room for a SPD too. However the cost of a shell of the consumer unit is so little compared with cost of RCBO's that go in it, likely cheaper to swap whole consumer unit anyway as you can then select one of the cheaper makes.
I realise that the idea that if some one can afford an EV vehicle they can also afford the EV charging point does not really work where the EV is provided by the firm you are working for, however the cost of EV charging points should be taken into consideration before making the change. I look at the homes in this village, and 90% don't even have a drive never mind a garage, a car park has been built for people to park their cars off road, but there are just two EV charging points, both 22 kW but switched off at night due to abuse. So most people in this village an EV is a non starter. I am one of the few who can park my cars off road, as long as it has a reasonable ground clearance, can't get Jag XE into main parking area at back of house as it grounds.