1. Use a low cal condiment on sandwiches instead of butter or margarine. I personally use extra low cal mayonnaise, aldi's own is the best one I've found as it's low in sugar too. Other ones might be a chutney (watch the sugar) or something like mustard.
2. Use a 50/50 bread if you can't face switching to brown bread. Watch the sugar again, Kingsmill is the lowest. This won't save you many calories but it's healthier for your body.
3. Mattesons turkey bacon is a good swap for regular bacon. It actually crisps up better than regular bacon and is about 1/4 of the calories.
4. Swap beef mince for turkey mince.
5. Instead of oil when frying, dry fry but use splashes of stock to stop your meat drying out. Water will do but stock adds more flavour.
6. Low cal mayonnaise is great in mashed potatoes instead of butter and milk.
7. When roasting veg, such as potatoes, instead of using oil, line a baking tray with baking paper. The veg won't stick to it like foil, but will still go crispy.
8. Swap rice or pasta for couscous. It's easier to cook and lower in calories. If you soak it in stock it's also really tasty.
9. Switch from low fat yoghurts (they're high in sugar) to Greek yoghurts. Again, aldi do a great Greek yoghurt which is only 70kcal a pot.
10. If you love a bit of cheese, try switching to a strong flavoured cheese, such as parmesan, but use less of it.