Laparoscopic gastric banding is usually done to aid weight loss. It uses a synthetic band to reduce the gastric (stomach) volume which means you feel full earlier and eat less. It is remarkably effective in well motivated individuals and has 'cured' type 2 diabetes in many patients as the diabetes is essentially caused by obesity. In many centres in the UK you have to demonstrate that you have lost weight by dieting before you will be considered for banding
I can't see that the CAA will have any major objection to the surgery, except saying that you have to be fully recovered from surgery before flying. It is worth remembering that any laparoscopic surgery involves inflating the abdomen with CO2. Most of this is let out at the end but some remains. Obviously at altitude, this gas will expand but as it is reabsorbed quite quickly, it will take longer to recover from the surgery than for the gas to be absorbed
Post-op there is unlikely to be any major complications that would preclude flying unless you were diabetic beforehand as glucose control will be affected by the change in diet and you may find hypoglycaemic events are more common
Hope that helps
Bob