Problem solved with the help of a good friend on site
If you are using wireless N you have to input the IP address to get the Printer and the PC to talk to each other. The wireless then works on the lower 2.4GHz 'g' bandwith.
Not exactly as per the manual but it all works in W7, Vista and XP
Incidentally I have learned from Canon they have no plans to change to wireless N in their multifunction devices as it would mean a major change to the internal hardware to improve on the 2.4 GHz band. Seems strange but that is their policy apparently. Case closed