Hi bottle. It's great that you want to lose weight. However, it takes time to put weight on and therefore time to take it off so please, if I can stress one thing, be realistic about how much weight you will/may/should lose in "a couple of weeks".
On a very basic level weight is a balance of calories in and calories out. To lose weight you need to use more calories than you take in, thereby creating a deficit. So, initially I would ask myself why I had gained weight recently, what triggered you to eat the crisps,chocolate etc? Try to understand your triggers and find ways to work around them.
OK, with regards to your food. Museli is stuffed with sugar - even the low sugar options are full of sweeteners. Raisins are also concentrated sugar nuggets
- great for quick bursts of energy but not great for weight loss. Try to maybe eat protein for breakfast with some veggies/fruit ... bacon and eggs, bacon and avocado.
No idea what a Costa lite is but anything 'lite' tends to indicate sweeteners. Again, may not have the calories but they still raise your dependency on sweetness.
Salmon is great for lunch but add in veggies, lots of them. Steer away from potatoes as they are full of starch. Not saying don't eat them but rely on veggies (especially green ones).
Snacks: no to snack-a-jacks. Eat a handful of almonds with a banana instead. Fruit is good but it is full of sugar (fruit sugars but again you are retaining your sweet tooth here so will seek to get your 'fix' from fruit and possibly over eat it. Also, fruits are not all equal - berries are much better for you if weightloss is your goal.
Semi skimmed milk - meh! I don't drink milk or eat dairy and my bones are fine. I am mid 40's and do eight bearing exercise to promote healthy strong bones. However, if osteoporosis is a worry to you (having it in your family) then take a calcium supplement.
Oh, btw, your extra exercise (taking the stairs etc) is brilliant. Try to get as much of this in your day as possible. Also, add in some lights weights and things like crunches and press ups.
So, sorry for the lecture
. This is not meant harshly but you asked for advice and this is my business (personal trainer).
PM me if you'd like more advice/help. Can advice exercises if you want.
Btw, you are taking an amazing step in owning this problem. Take it easy, don't try to lose a stone in a week. You will get to where you want to be - be kind to yourself. Good luck.