It is officially not allowed, but it will work well on a 16A extension cord. Note that the box will be about 50 cm from the plug, which will shorten the effective cable length. Your best plan would be to keep the cable and box in the boot and run an extension cord into the car and the charging cable out again, for instance through a partly-open window. It would prevent theft as well.
I charge my car, which is in the drive, through a wall charger and a 20 m charging cable. At work I use the wall socket method.