Hello, sorry I only saw this now, I should come to this part of the forum more often!
I am doing Slimming World and while it is not a fast diet, it super super easy to do. You are never hungry and you can eat as much as you want without weighing and counting.
The basic principles are that there are three types of foods. Super Free, Free and Syns.
The rule is that of each meal you should eat 1/3 of super free foods and the 2/3 of free.
Super free foods are most fruit (but not smoothies, or cooked fruit!) and most vegetables (including passata and tomato puree for example).
Free foods are things like all lean meats (including ham and lean bacon!), poultry and fish (even smoked salmon, but not smoked mackerel, too oily). Also rice, pasta and potato and pulses and beans.
You also have Healthy Options A and B allowances per day. Healthy Options A are dairy products. Milk and cheeses are among those. I really like my coffees so I use my daily allowance of Healthy Option A for 350ml skimmed milk. But if you don't need milk, then you could exchange that for 35gr of cheese for example. Not a lot! And this is per day not per meal! (But most Non fat things such as most Muller Light Yoghurts, Low fat Cottage Cheese and Quark are free food!)
Healthy choice B are things like cereals, wholemeal bread, dried, canned or cooked fruit. I choose 2 slices of wholemeal bread (from a 400gr loaf!) a day for my allowance. All other breads (non wholemeal) are syns and need to be counted as that.
And that brings you to your syns, short for synergy but pretty much like a sin or treat

. You can have 15 syns a day and you should not skimp on those or you will start to feel deprived. Syns are things like butter, oil, cheese but also chocolates and sweets etc. This is where the online resources for Slimming World come in useful as it is really hard to know what is a syn at times and what isn't.
I usually have my Dolce Gusto coffee in the morning which has 2.5 and then a Freddo chocolate in the evening, which has 5. I may also sometimes have a Grande Skinny cappucino at Starbucks, which is another 4.
As for cooking oils, you can use the 1cal frying sprays and I swear roast potato (free!!) tastes just as nice! Oh also free are Baked Beans would you believe!
It is difficult to include everything here that you can and cannot eat on this plan but I hope I have given you a bit of an insight. I go to meetings every week and I must say I enjoy the me time.
I would strongly recommend that you do join. Some ladies in my group have been sent by their GP. But I am thinking your BMI has to be a certain number for you to be referred. but I know that the NHS does sometimes pay for it.
If you cannot afford it then I would recommend you look for online meal recipes and other info, for example on youtube as I know there is a lot of that floating about.
Good luck
btw I think you have the costs wrong: as far as I remember it is £10 to join and then £4.50 weekly. But they do sometimes have offers on, so watch out for that. https://www.slimmingworld.com/joining-a-group/special-offers.aspx