Why are mortgages haram?

I know taking loan and mortgage in haram in Islam. In UK, I am paying the amount of money as rent which I can pay as mortgage. If I pay as mortgage I will be the owner of that house after several years. But paying the rent I have to pay in this manner for the rest of my life and never be the owner a house. In this time, it is quite tough to pay all the money all at a time. I know related the punishment and warning related to what Quran and hadith has said. Actually I want to know inner meaning why mortgage is haram in Islam. What are the bad consequences of taking mortgage? What is overall effect? I want a clear explanation.