even if it was possible to members of the public to have food analysed in this manner, what good would doing it do you? I presume from your post you have thrown away the wrapper and even if you havent how would you prove that the food you had analysed in fact came from the packet that was "wrongly" labelled? For example, if it was pork you didnt eat and you bought what was labelled as a packet of lamb but actually was pork, who's to say you didn't buy some pork and claim it was labelled as lamb. Sueing people is an expensive business and probably for very little reward, as you may not have actually suffered any physical damage from this incident. if it is more of a religious or cultural thing, how will money compensate you for that?
it would be like saying my religious beliefs were compromised, but ehy, bung me some money and it will all be ok.
In My opinion, you would be better off going to wherever you bought it from and pointing out their supposed error and seeing where that takes you - perhaps some compensation n the form of a few vouchers?