Apparently the owner of the car is complying with the law, as the cable was yellow and therefore could easily be seen. So he or she is not obliged to do more.
I understand your concern, though, but apart from taking the entire matter up with your local authority, or you MP regarding further safety precautions, there is not much you can do.
Nor can I personally think of anything that would lessen the hazard of people tripping, unless the cable is fixed in place with duct tape.
Certainly, a sign saying "Beware of cable crossing pavement" or the like would help those of us who have reasonable eyesight, but is no help at all to the partially sighted or blind.
In the long term, I imagine it will be illegal to just plug in a flex in your house and run it across the pavement to your car, and that owners of electric or hybrid cars will have to either re-charge them at a parking place that has a power point, or make a driveway onto their property.
So the way forward might be to petition your local council for kerbside electric power points like those you see in marinas. Whilst you are at it, would you mind asking them to provide power-points for electric bikes too? They are in very short supply, I can assure you.