I do this! Helpful tips:
-Keep your food in a different place from where you spend most of your time. For instance, if you keep your computer in the living room, try and make sure you can't see the kitchen, and don't keep snacks next to it! Then you have to get up to get a snack, so you're less likely to just absently munch.
-Popcorn. I don't know if they've got the 100 calorie bags in the UK yet, but they have them here in the US and it takes me a good hour to finish a bag, because I...
-Eat slowly! Eat one kernel of popcorn at a time. Even if you're eating chips (crisps), don't take huge handfuls at once and they will last longer. If you need a fruit, try raisins or grapes, and you can eat just one at a time so it takes a while to finish. Or for veggies, try cherry/grape tomatoes. My biggest problem is that I have somewhat of an oral fixation
So I like to always have something in my mouth! So if I eat small, healthy things, it doesn't add up so fast.
-If you have a day where you really just want to snack, don't plan any meals. Whenever I spend a whole day munching, I skip dinner because I've had the calories already.