Tell me why?

Another totally unoriginal post-holiday observation – why do so many grown-up English people insist on wearing football shirts all the time?

I can understand the club shirt thing – if you are from Newcastle and hoping to bump into some other Geordies in Spain or wherever then wearing a black and white striped shirt will obviously help. But England shirts? Is there a reason why English people want everyone to know, at all times, that they are English?