Done this lots of times before but I'm stumped this time. The top of
each tap has a small colour insert- but no obvious means of prising it
off to get access to the retaining screw (if there is one underneath).
When the tap is fully opened it reveals a collar which can be unscrewed
to give access to the "works" but I imagine that the top of the tap
should be removed first - am I wrong?

Ian