I can't find the little silver part that came with the mixer tap when I purchased it before I put in the shower head on it. Does anyone know what this is called. It's the part where you can choose if you want the shower connected to the taps or not so you can isolate it
The part you seek is very probably called a selector or something similar - to direct the water to either the tap outlet or to the flexible hose and the shower head - the control handle of a two way valve.
First the manufacturer - then the model - then the part itself.
You might consider using Google and selecting images and enter the phrase Shower Mixer Tap
When you see an image similar to your mixer follow the link for more information.
Then contact the manufacturer for parts availability.
Alternatively - search the house to find out where you put it.
Good Luck...
November 2015
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix plumbing.