I confess I'm not a fan of Slimming World. They don't prepare you for the simple fact that if you are smaller, you need to eat less. So, of course, you shift all the weight but are still used to eating a
lot of food. Sure it's "free", but it ensures that your stomach remains large, instead of shrinking as it should. Upshot? You still eat a lot
If you eat smaller portions, cut out snacks, etc, eventually your stomach shrinks back down, and suddenly you find you just can't find anywhere to put that Chicken Tikka Masala with Pilau Rice, Peshwari Nan, Bombay Aloo, and Sag Paneer. Which is good, because it means you start eating like a thin person - smaller meals - and it comes naturally.
100 people will give you 100 different pieces of advice about losing weight. And some will seem contradictory, which doesn't help at all. My advice is this:
Don't panic
You're not alone in the amount of weight you want to lose. I want to lose over 10st, and others on this board want to lost 15, maybe 20st. Don't worry about
how much you want to lose. I guarantee you it's irrelevant. Panicking about the big number allows it to look all scary and impossible.
Look at it this way: 8 stones? You can get rid of that in a year, or a little over. Start today, and by this time next year you could be either the weight you want, or very close to it. But if you never start, then you'll reach this time next year, and you won't have lost a single pound.
Relax

You can and will do it. 8 stone? Pfft. That's 112 pounds. A good, healthy rate of weight-loss is 2lbs a week. If you lose 2lbs a week you'll lose 104lbs in a year, leaving you all of 8lbs to go, and you can budge those off in a month.
Lots of people will say that you don't have to give up chocolate, sweets, crisps, etc. And they're right, in a way, but don't let that lull you into a false sense of security. If you want chocolate, have a small one rather than a whole bar. If you want to avoid fatty foods, just don't buy them or have them in the house.
Refined cane sugar is excruciatingly bad for you, because your body starts to think your blood sugar's too high... so it releases insulin. And when the artificially-introduced sugar is out of your bloodstream (which happens very quickly with refined cane sugar), you're left with a sugar deficiency because you've too much insulin in your system... So you crave sugar. Which makes you produce insulin... which makes you crave sugar... and so on, and so on. If you
can cut out the sweets and chocolates, it really is the best bet. You'll find you're more able to indulge once in a while in a small chocolate or just one sweet if your body isn't in this constant faux-diabetic state which can very easily lead to real diabetes.
Keep hydrated. Most people feel hungry when all their body needs is water. Don't forget that your brain also takes 20 minutes to realise that you've eaten and to switch off the hunger-nagging, so try to eat slowly: Do not load the fork for the next mouthful until after you have chewed, tasted, and finally swallowed your current one. Do not eat while distracted or have a limited amount of time - watching TV, working at a computer, riding the bus, and so on. Pay full attention to the food that you eat, the taste, the texture, chewing it and swallowing it. Don't ever eat on automatic, because part of what tells your brain that you've eaten is your chewing and the flavour you release when you do so.
As for a gym routine? Well, that's easily done. Join a gym. Any gym should offer you not only an induction, but an initial fitness plan or two. They'll sit down with you and ask you what you want to get out of going to the gym, and your answer is simple: "I want to lose eight stone in a year."
They'll walk around with you, get you to try various pieces of equipment, and work with you to create an exercise plan. Most gyms will also give you a reassessment after a month or two to adjust your exercise plan to your new fitness levels. On top of that, all gym equipment is adjustable, so if you find your routine is becoming too easy, you can crank it up manually then speak to an instructor to have your plan adjusted.
My local gym is actually excellent for this. They have Technogym equipment with something called the Wellness System. What this means is that your fitness routine is stored electronically on a key that you are given. You insert the key into the equipment, and it automatically begins at the pre-programmed routine, and when the routine's session ends it tells you what the next piece of equipment is that you need to go to. If you find the routine getting easy, you just ask one of the staff and they re-write your program in seconds, so the next time you turn up and insert your key, it's all automatically moving to your new routine
Short answer: Eat less, cut out the fatty food, replace snacks with fruit or veg, and exercise more.