I gave my cat a spoonful of chocolate milk (remainders of cocopops) will he be ok??

Not a good idea. Chocolate is toxic to cats and milk can give them loose stools. A spoonful will probably be ok, but do not do this in the future. NO chocolate.

your cat will be just fine

Yes he'll be okay, just don't give him any more. It is lethal to give cat or dogs chocolate, but only in somewhat large portions. A spoonful of chocolate milk is fine, don't worry about it :)

It's not a good idea.

It wasn't the best choice but the amount of chocolate actually in the milk is negligible. If you want to give him a spoonful of milk occasionally as a treat, give him plain milk, as the sugar in the milk from the cereal isn't good for him either.

You shouldn't have done that. But he should be okay... Any signs of illness eg throwing up, not being himself then take him to vets

yes, but dont do it again,