Any animal that has a cloven hoof that is completely split into double hooves, and which brings up its cud, that one you may eat. … And among the birds, you shall hold these in abomination; they shall not be eaten as they are an abomination … (Leviticus 11:3, 13)
While the Torah goes on to list a number of birds which are not kosher, the Gemara says that a hunter is always believed if he says that a particular bird is kosher, provided that he has a tradition from his rabbi that it is acceptable. Rabbi Shlomo Yitzchaki (known as Rashi, d. 1104) explains that this means we can only eat a bird if there is a tradition that it is kosher.
One example of a bird for which there is some discussion is the turkey. The Shulchan Aruch (Code of Jewish Law written in 1563) states that provided a bird exhibits three signs, it is kosher even if there is no tradition, implying that it is permissible to eat turkey (Yoreh Deah 82:3). Although Rabbi Moshe Isserlis (known as the Rema, d. 1572) disagreed, most authorities are lenient.
Rabbi Yosef ben Meir Teomim (known as the Pri Megadim d. 1792) says that even if one is strict and abstains from turkey, the issue of tradition only applies to birds. Therefore based on the first verse, any animal which chews the cud and has split hooves may be eaten, even if there is no tradition to.
One such animal is the bison, known in America as buffalo. Some kashrut authorities in America have ruled leniently, permitting buffalo meat even though there has never previously been a tradition to eat it.
While it is not unknown for buffalo to be farmed in the UK, it is not generally found in the wider market. Kosher buffalo meat seems to only be available in the America although buffalo mozzarella (made from buffalo milk) is apparently available in some kosher shops in the UK. It may therefore only be a matter of time before we can enjoy buffalo burgers without having to take a holiday.