No their is no larger cables outside. The cables leaving the meter box are the same overhead all the way to the house. I will try and get some pictures of the house bracket connections at some point. If I were to talk to the electrician again what might it be good to understand, perhaps the size of the cable he would want to bury and how much it would cost. Obviously, you have all said that a large cable would be needed and that it will cost. At the end of day I have been pondering why on earth would I pay out to have a cable buried. Why not wait for something to happen to the overhead cables then fix it? Would an electrician turn a blind eye to the overhead cable and get on with the work for the extension?
Not a proper one.... One of the main regulations that we work to is that the work that we do and what we connect it too must be safe.... If it's not safe then.....