Well, I went round tonight with a print out of the replies here and here is what we found.
Undid one of the 2 screws holding the muzzle brake clamp. As soon as it has released the whole muzzle moved about 1/4" to the right as you look from the breech end. After sliding the assembly off then spent nearly 10 minutes seperating the clamp from the brake.
The screw is still in the clamp part as it seems to be stuck in there. Do not know the thread size so the appropriate grub screw can be used?
They will be trying tomorrow getting it zeroed at 20yds for wind. they will also check it on Saturday and then Sunday. If the windage does not move again then all is well. He has also got a ABS case now not the soft version.
Will keep you updated. Thanks again