The balloon I cant help you with, but the NHS thing I maybe can. Glasgow, likely you will be entitled to help on the NHS. They seem to follow NICE guidelines. Edinburgh I'm not sure about. Anywhere further north than that, unless you have considerable co-morbidites you aren't likely to get help based on a BMI of 40.2. Most of the Highlands refer to Grampian who will only do a BMI of 60+ or 45+ with Type 2 diabetes. Tayside I believe wont help anyone unless you have significant co-morbidity's regardless of your BMI.
If you are serious about WLS the first thing to do is work out what PCT (which NHS board) you fall under for where you live. Then contact them through the freedom of information act and ask what their guidelines are.
Next step is to talk to your doctor. Whether you meet the guidelines or not, speak to your doctor. Ask for a referral and if you are rejected ask for tests, Diabetes, Sleep apnea e.t.c
Only once you have eventually been referred will you get an idea of which procedures you could get. If the balloon isn't available in your area (and tbh I don't think its widely used up here) you could look into alternatives, the sleeve is really popular and obviously the band. I think the band is easier to get, there is a central Scottish hospital who I believe take band patients from across Scotland so that is likely to be an easier alternative.
Whatever happens, I wish you lots of luck! At the minute I'm fighting for help through my MSP as I was rejected even when my BMI was 51. But thats in Aberdeen and the NHS board here really sucks. Don't give up whatever the doctor says, there are lots of ways you can fight around funding on the NHS. For the balloon in particular if you can find an area that does perform the Balloon and you are prepared to travel, you could ask for a referral to that hospital, But this wouldn't work for being referred to Glasgow as they don't take referrals from outwith the area unless you already live there, in which case your probably fine!