Given that there is an undeniable link between ultras and right-wing extremism, this was most likely done as a political statement more than a loophole. The reasoning being that sooner or later someone is going to do something illegal while wearing a Niqab and it will force the government's hand. You people might find it hilarious, I honestly find it distasteful. Now while there's plenty to say about Islam (and I don't want to get into that discussion) I think we can all agree that people shouldn't have their religious rights infringed because a vocal/violent minority can't behave themselves while watching football.
It's also disgusting how much support there is for ultras in this thread. I love football. As a Chelsea fan whenever I visit Stamford Bridge I always sit in the Lower Shed, one of the most hardcore areas in the stadium, simply because I love the atmosphere there. But ultras, and especially the violent ones, are a blight on the sport. It is possible to be passionate about football without behaving like a twat.