Thank you so much for this very informative advice.
My hen eats exactly the same as the other two and they have never given a double yolk egg. They have their mixed seed dish in Their coup for early morning feeding as we are a bit lazy getting up, they then have a small dish of pellets, about a mug full for the rest of the day when they then free range in the garden, we have 2,500 sq meters of land so plenty of space which keeps them occupied for the day. In the evening they get a cereal bowl size of a mixture of wheat, tinned sweetcorn, and raisins between them, oh and a pot of yogurt. We dont tend to have much left over food from meals so they get very little table scraps. Because they are so active all day, especially when I am weeding in the garden as they follow me everywhere in the hope of lots of creepy crawlies to eat I dont worry they are over eating.
Today, she laid her first egg, quite small so I dont expect it to be a double yolker, i would be more than happy for this to be the norm and an extra big egg now and again as a treat. Hopefully she will have a long and happy laying life