I didn’t mean to sound rude, OP but your posting style is very erratic and you don’t seem to be taking advice on board, which is why I mentioned it. If the NHS website tells you to eat in that calorie range, then do just that. I don’t understand what the issue is. It’s a long slog losing that amount of weight and while it might be tempting to cut right back on calories, this is not sustainable in the long term.
In terms of how you can improve your eating:
Breakfast: special K is just empty calories and sugar. Try scrambled eggs with veg, smoked salmon on rye bread or porridge with berries and a few almonds instead.
Lunch: if you’re doing lower carb, have full fat rather than low fat Mayo. Maybe add an egg in as well. If not lower carb (which is probably best if you’re doing a lot of exercise), have some potato, oatcakes or a slice of rye bread.
Dinner: either have more burgers and veg cooked in oil or add some carbs to make the meal more substantial. Try to have some protein - fish, chicken, tofu etc and plenty of veg.
Snacks: go ahead biscuits are full of sugar so try something like hummus with carrot sticks, a handful of nuts or full fat Greek yoghurt with berries.
That sort of diet, combined with regular exercise will keep you satisfied and able to sustain over a lengthy period of time. I don’t know what your goal weight is but if it’s say 11 st then you’re in for quite a long journey so anything faddy is unlikely to work. Also, it needs to be a way of eating that you can continue for life.