I use my fitness pal every day. It is an American site, so the way to make it easier is to type in either the brand name, or the supermarket name then the product. American measurements tend to be in cups or ounces, so if one of those comes up, that is probably an American item. UK items are usually grams and slices, but this is not always the case, so be careful or you could end up with the wrong information.
Check the products like Claymic does, to ensure that you are on the right track. As you use items they are saved onto your food lists, making it easier to know the right ones for you. You can also add regular meals, that is also easier as your own items that you know are right carb wise are used.