Thanks for prompt response.
Just one follow up question:
1. is it a 1inch Mi Straight washing machine tap isolation valve that I need? I ask this as the link you gave was to a 3/4 inch valve - whereas the end of the compression joint on the dishwasher intake pipe is 1 inch.
In response to your question - a gully trap drain already on other side of wall to where dishwasher is being installed - just need to break through wall with outlet pipe.
I have the large grey aquastop. It's opening measures 1 inch across.
Thank you that is just what I needed to know.
Just spoke with my Dad - he is going to have a root round in his store to see if he has one that he can bring along tomorrow.
Thanks again for your help.