For the Chocolate Banana Muffins it states "large" eggs but in the US "large" are equivalent to "medium" eggs in the UK. So is it large UK or large US?
For Nigella's Chocolate Banana Muffins (from KITCHEN), and for many of her recipes, the egg size is the same for both the UK and the US. There is a small difference in egg sizes between the UK/Europe and the US, but so far we have found that using UK large eggs and US large eggs in the same recipes has not caused any problems. So you can use large eggs in the UK and also large eggs in the US for the muffins.
In addtion, there is some crossover in the egg sizes. European large eggs are 63-73g and US large eggs are the equivalent of 57-64g (the legal size grading is set out in ounces: 2-2¼ ounces). Consequently, the smaller end of European “large eggs” can be the same weight as the larger end of US “large eggs”. It was decided to use the same egg size for the US and the UK to make the recipes easier to read on-screen when moving between UK and US measurements.