Depends where you eat in Britain. Been all over Britain, and a number of places do feed you very well. Especially fish and chips places (my favorite eateries) which are on average easily superior to American fish dinners. And you get about as much food but it tastes better.
Meals in Ireland were good and plentiful as well without asking for extra-sized portions. FYI, I didn't eat nothing but f and cs. I ate other types of food which on average were good and plentiful as well. Shepherd's Pie...yum yum.
Euros are beginning to get fat as well.