Millions of Americans eat Kosher food all the time -- even Muslims and atheists. The food doesn't taste any different, it's simply been blessed by a rabbi.
If the poor little Brit-brats are eating sloppy-joes from a halal-approved cow-slaughter, then I'm not terribly worried. These ignorant parents would spend their time more wisely electing a government that was resisting Sharia law and not pulling its troops out of Iraq.
This is just easy-to-be-mad-about fluff.
I did some looking on the net and halal isn't much different from kosher. Kosher beef starts with a cow being slaughtered and drained of it's blood in the same way as halal slaughter. The things I read also said it's not just a rabbi's blessing that makes something kosher but the way it's prepared or inspected, so just blessing something isn't enough to make it kosher. As far as the school controversy goes, I don't know if it matters much except for the aspect of bending to the will of immigrants at the expense of a native population. I imagine halal prepared food commands a premium price over 'regular' food.
Kosher is not food "blessed by a rabbi." In the most general terms, it is something that is certified by a rabbi as being in accordance with the law as set forth in the Torah and in Jewish tradition (which may mean slaughtered, or cooked, or grown, or of the substance, or made, etc.). "Blessing" has nothing to do with it. Moreover, just as pork is prohibited under Jewish law, it is also forbidden under halal, which is derived from the Torah (i.e., the Jewish Bible, the Pentateuch, or Old Testament to Christians). Thus, many old traditional English "delights" :-) such as bangers and mash, would not be permitted to be served in an English school that imposed a halal menu on its students.