In the US 'medicated feed' contains something calle Amprolium - it is very sfe and simply blocks thiamine metabolism that is essential to the life of coccidia and less critical for the chick.
So in the US it is safe to eat eggs from chickens eating medicated feed but it is intended to be used only for the first few weeks of a baby chick's life.
I did once get a bag of medicated feed by accident and everyone ate it with no ill effects.
But you should check what 'medicated' means in the UK because if that means they contain actual antibiotic drugs then it would be a different story.