Remove basin tap head?

We have Armitage Shanks Millenia taps in our bathroom. The cold tap on the basin revolves but does nothing. I want to take the tap head off, but it is not obvious how it comes off. There is a sort of domed cap, but that doesn't want to come off, or just under the grip, it may unscrew, or possibly the whole head just pulls off. I don't want to damage anything, but I cannot see how the head comes off. Any advice greatly appreciated.