planning regulations for farm shop

Hi, does anyone know where I could get information on planning regulations regarding a farm shop which produces its owns products ie breads, savouries, deserts, jams chutneys etc and also has a gift section. The shop is only open one day per week in an existing garage on a farm. I thought that when it was your own produce you were selling that there was no need for planning permission, however, the council say we have to get planning permission. They have said to us that there is something in regulations about farm shops but refuse to meet with us to discuss it. I would be very grateful if someone could point me in the right direction regarding getting info on farm shop planning regulations