Corkers, Mark! You really hit the sweet spot using the teleconverter on the GR.4! Love the black and whites.
P_J is correct. The GR.4 is ZG752. You can just make out the serial on the first image, and the code (129) on the tail of the third image.
Image of ZG752 caught at RAF Marham a couple of months ago.
http://www.!!!!!!!!!!!!!!/photo/UK---...GR4/1299296/L/
Cheers
TJ