At your weight, I would eat 1, 800- 1,900 cals a day and start exercising as much as you can. Moving those 5 extra stones more than usual will quickly burn through calories, and the advantage of this method is that you are learning pretty much what normal portions are. You will be able to up your calories by about 100 on a permanent basis once the weight is lost.
Focus on healthy eating and keeping a very close eye on portions. Especially with 'healthy' foods like muesli or nuts. A big bowl of muesli with milk can be 600 cals. A small handful of nuts can be 300 cals.
Think about foods you like that are also healthy for you. What are your favourite veg, fruit, lean proteins etc?
I would advise you to cut right back on refined carbs and sugar, just because they can trigger cravings that aren't hunger but feel like it. And up protein as that helps you feel full longer.
Work out a handful of breakfasts, lunches and dinners that are roughly 300, 500 and 700 cals each, so you have some wriggle room for cups of tea with milk and a small snack or a glass of wine.
An example:
Bagel thin with poached egg, a piece of fruit and coffee with milk for breakfast.
Veggie soup with a piece of cheese on toast for lunch
Baked chicken thighs with roast Mediterranean veg for dinner, with herby couscous and leaf salad. Slice of melon or bowl of strawberries.
If I have a sweet tooth after dinner, I have a Jude's fruit ice lolly - only 24 calories!