I bought one of these Honda aerials off eBay which I have fitted to my One Convertible

Now I want one for my Mum's 2003 tintop One as well but I can't seem to unscrew the standard aerial

Is it a different fitment, it looks like it might be moulded on to the base?
I'm a bit confused as other people seem to have fitted them to their 2003 MINIs. Is there something I'm missing?