Thanks everyone for your helpful responses. (I have now shed my cloak of anonymity - i.e. worked out how to register).
But since we've accidentally wandered off, can someone explain a bit further? I thought that every http access started with a HEAD in order to get the content-type - which is why I was so trusting of Gisle Aas's advice. Clearly I was wrong. But where exactly have I strayed from the path of righteousness?