Alright. Here's the correct answer.
Those of you who think that Blair had a point would not make the same argument in support of banning the Yarmulke, the sari, the tutu, etc. You're focused on the veil. Why? Because it's a muslim thing.
As an aside, it has little to do with "being foreign": many, and probably most, of those who wear veils are native-born (i.e. born in Britain) and young. It is the equivalent of the revival of pentecostalism here. Unless, of course you want to tell those that have immigrated, say, thirty years ago that they cannot wear the veil, and that their children can. The would be an interesting position to hold, but I think that it would strain your intellectual resources to defend it.
Okay, so those darned muslims. Being a muslim thing isn't enough to hold your attention, though. You would presumably not want to force muslims living in Britain to, say, eat pork. (Although, the definition of Libertarian is so flexible these days that who knows, maybe you would tell them what to eat as well as what to wear.)
In any case, let's assume that you'd be willing to let them eat pork. So, back to the veil. Why the veil? Let's speculate a little. Maybe you think that veils are worn by "fanatics" who are going to "blow you up". Is that it? Kilts are jolly and veils are scary? Are those great big beards that the men wear scary too? Shall we chop them off? And, because we can't tell the difference between a sikh and a muslim, should we have all those Sikhs in London and Birmingham, Oxford and Bournemouth, York and Cardiff unfurl their turbans and cut their hair? Just in case?
That's kinda a good starting point for a discussion.