What the law regarding selling day old chicks? or POL?

Hi all, Happy new year (I dont think its too late to say that)

I am wondering if someone can tell what the law is regarding selling day old chicks and POL chickens fom my front door. Im starting to sell eggs to local villagers however I have had the odd request asking if I can get chicks or sell chickens. So far I have said none are for sale but I shall possibly be hatching in the future. So do I hatch to order? Also if I sell POL do I have to make sure they are laying or just sell them at a set age where they will be about to lay?
Am I required by law to vaccinate my chicks or POL's I sell? And finally isn't it a little wrong selling a day old chick? could all the transport and tempreture change kill the chick? Surely it would be better to sell them at 3days old?

Also a local cafe has expressed an interest in my eggs however I said im not too sure on the law and didnt want to get into trouble. She shrugged her shoulders and said shes happy to take the eggs still, so will I be doing anything wrong by selling her the eggs?

Sorry for all the questions  Any advice is greatly appreciated

Thanks 

Also some people want the 1 day olds to put under a broody hen

A guy in Surbiton (where I bought my chicks) has a fairly thriving business, he is DEFRA registered, he sells Day olds and various ages of birds, various breeds, but he said he couldnt make a living at it and it messes up holidays, weekends, he is pretty up front about it, he knows people want hens, so he kils the cocks and freezes them for reptiles and such, I dont know if he sells them live for them
I 'll drop you a PM with his website address, and contact number

They are a lot more than that down south, and there arent many places I can find that sell POL or chicks, up to 5 days old