I don't mean to be a spoilsport, and good fun they as they may be. I would advise that if anyone were considering using or carrying a blowpipe or similar, that they do so in an area to which the public do not have access, otherwise they may find themselves atracting problems. Under the law, a blowpipe is an offensive weapon, in the same way that lock knives/bladed articles are, the difference is that there are much more reasonable explanations that may be given by a responsible adult relating to the carriage of a lock knife/ bladed article than a blowpipe, particularly if the blowpipe is carried with it's amminition.
Hope that this is of use.
Cheers