Following a few more ideas and a good coat of looking over we have moved the dish to a temporary location on top of the scaffolding at the rear of the property. Fortunately the existing cable is long enough once unclipped from the wall to go diagonally straight to the new position. The builder was able to use the existing bracket from the wall and mount it on an old bit of wood to clamp it onto the pole. Our final bit of good fortune is that it is high enough to receive a signal over the top of our new roof (when it is built) and that of next doors as well.
Eventually the dish will be moved again onto the gable end of the extension, this will require new cable but we will run that internally through the loft space rather than on the outside of the house with cable clips.