Many thanks for the comments Guys,

I was using the Canon 400D and the Canon 100-400mm is L series Lens,
as for the location from the visitors center cross the road to the fence walk down towards the BA base And I think it was the First set of Traffic lights stop about there and shot through the Fence ( take some thing to sit on) If not try the second set further down

I have to admit, once I had seen the images on the LCD of the camera , I was far from impressed due to the light conditions ,I even stopped taken pictures because of the lack of light, but on seeing the images on the computer I wish I had continued to shot
I Think we were lucky with the low cloud cover diffusing the light.

Kevin