How do I go about gastric surgery through the nhs?

I'm not a mively woah look at that big momma girl, but I am overweight and just can't shift it. I recently broke up with my fiancee and went through hell and didn't eat hardly at all only when I absolutely had to (couple of water biscuits were about it)!!but still didn't lose hardly anything. please don't be cruel just need some advice thank you xxx