Trying to remove taps on mixer unit

[gravesend46]

This is probably very basic - but how do I remove the cold tap on the mixer unit to fix a leak? Pic here:

http://imgur.com/BNIXr.jpg

I would have assumed prising off the blue circle and finding a nut/screw beneath but it doesn't seem to come off under a little pressure and I don't want to break it off before checking!

There is a grub screw in the central block which removes the spout but I cannot see any other obvious signs. I have removed the spout and the nozzle/aerator and the washers seem fine. Narrowed leak down (as far as I can tell) to the cold fitting as it's only with the cold supply on that the leak occurs, not with the hot.

 

[seco services]

i would say the screw is under the blue cap

 

[gravesend46]

Hmm. I've given it another go with a very small screwdriver trying to lever it up but it just seems to be taking chunks of plastic - the hot and (green) filter taps the same, no give at all.