Hi Guys, many thanks for all your good comments, I just thought I'd let you know the outcome!
It seemed most people were suggesting the rotor so I took a closer look, I fired a plumb laser on the leading edge and gradually turned the wheel, the rotor was straight as a dye - or so i thought!!!
I then tried a gauge which measures to the 1000th of an inch and found that there was a bow in the rotor of 3000th of an inch (0.0762mm); I flexed it back into position so it was within 1000th of an inch (0.0254mm) across the total perimeter of the rotor.
Put the wheel back on and tested in out, not a vibration to be felt.
I am absolutely amazed that the rotor would have to be this accurate so no wonder every time I visually looked at it, it seemed in perfect alignment.
I am also amazed with how easy the rotor was to flex back into the right position so I'm now very paranoid about knocking the rotor and ending up with the same problem but for now it works perfectly.
Thanks again to you all for taking the time to comment.