I have a Blanco tap. In my case, there is a small red and blue cap which I removed to reveal a small grub screw. Undo the grub screw with a small allen key and the tap top will come off. Undo the chrome plastic cover to reveal the large metal brass nut. Turn off water mains for both hot and cold and remove brass nut to reveal tap mechanism cartridge. Replace cartridge and reassemble as above in reverse. The whole operation takes 10 minutes with the right tools.
Paul, Manchester, May 2009