Gas Suppliers

When you switch gas suppliers, who actually owns the gas pipes and how do they know how it is in there??

It is not how much is there but how many passes through your meter, I suppose, as the property that comes when you take a contract with a particular supplier. The question is crazy, to whom they belong, if you do not have a contract with a particular supplier and they are not accustomed, I suppose again if they are on your property, you own .. good, to ask local gas man ..