Loz - I would advise avoiding all diets and pills.
What you need is a sustainable eating habit. There are so many myths about weight loss and exercise but the science is really quite simple - "eat less - move more."
You have to consume fewer calories than you burn, it really is that simple. Be content to aim for losing about half a pound to a pound a week. One pound in weight represents 3500 calories which is quite a big deficit.
Go and look at a half pound packet of butter and imagine all of that coming off your body every week.
Most of us eat far more than we think we do. Cutting down on snacks and sweets is really important. Start the day with a breakfast that will keep you full for hours. Porridge is excellent as is a "low GI" food. This means it won't peak your blood sugar levels as it releases its energy slowly.
Think about the calorie content of what you eat. Ignore labels like "low fat" they are often packed full of sugar. Its all about calories in and calories out.
Do not starve yourself. Eat smaller portions frequently. If your body gets the message there is a food shortage it will go into starvation mode and hold on to its fat.
When people claim to have lost large amounts of weight quickly it is almost always down to water and glycogen. The fat cells will have shrunk but are still there and will quickly blow up again when you re hydrate. Be patient. It took a long time to put the weight on its not going away in a few weeks. Your body is programmed to protect its emergency energy stores.
All of us use a certain amount of calories even if we didn't move a muscle for 24 hours. This is called our basal metabolic rate. Muscles burn much more calories than fat so if you can manage some simple weight training your muscles will burn fat for you even when you are at rest. Don't be taken in by claims about "slow metabolism" its just an excuse. Very rarely people have a genuinely slow metabolism, a medical condition that is easily diagnosed and fixed.
Take every opportunity to move around. Even just standing more than sitting will make a difference. Take the stairs rather than the lift, park your car at the opposite end of the car park etc. There is no need to take up jogging. Calorie control is the more significant part of the equation but anything you can do to increase the amount of calories you burn each day will help. Walking is effective but try to increase the pace. The first 20 minutes of exercise does little or nothing for burning fat - your body will be running on glycogen and only burns fat reluctantly. Its the next 10 minutes that make all the difference.
Lots more I would like to share but hope this helps.
One last thing - don't get obsessed with the scales. Weigh yourself once a week at most, always first thing in the morning. The more important measure is you will notice your clothes getting a bit looser.
Good luck and don't beat yourself up when you have a bad day.