I've been working at a house (1930's semi in a 30's built estate). I looked at the fusebox and noticed a supply neutral and phase but no earth connection. The supply cable to the head looks like something covered in bitumen/tar. The earthing is made by clamps onto the incoming metal gas pipe and lead water main. It has been rewired in the 60's but still retains the 4 way rewirable fusebox. I thought all old houses had an earth supply,please tell me more (it's in south london not a country area)