Here's an eyewitness report of sorts for you.
At the time of the accident the airfield was in brilliant sunshine however a fog bank could be seen around the 15 threshold (viewed from the Elmdon Building (old terminal). Myself and colleagues had watched the previous landings (a BEE DH8D and AUR AT72) disappear into the fog on short finals and emerge well over the runway. We commented that we were surprised they hadn't gone around, especially the ATR. Comments from those crews would be illuminating.
The fog was purely at the 15 end and we were actually questioning why ATC were still positioning traffic for 15 when the 33 end was in the clear and the wind negligable. The fog bank was steadily moving along the runway, hence the rapid drop in touch down RVR. I didn't see the Citation on approach or hit(?) the ground but did see it emerge from the fog nose pointing away from the runway and saw a rapid fire and a very large plume of black smoke (I assume this was as it hit the 15 GP aerial). A few seconds later it was obscured by the fog. There was then a delay of several minutes before the fire service turned out which lead us in the office to question what we had actually seen, particuarly as the aircraft could no longer be seen because of the fog
From my viewpoint the fog seems to have been a serious factor here with a rapid deterioration of visibility at low level. I cannot say what the touchdown RVR was at the precise time of the accident but it had been above CAT 1 imediately before, but within about 10 minutes of the accident the whole airport from our viewpoint was enveloped in thick fog although the Helimed Agusta from Coventry let down visually on the 33 threshold but could not be seen from the tower.
From my perspective the two areas of interest would be the rapid loss of visability around the 15 touchdown zone and the initial confusion and delay in responding to the accident, probably the sudden loss of visibility played a part in that?.
After seeing the above I cannot tell you the relief at hearing the Helimed depart to Walsgrave Hospital and seeing an ambulance leave on blue lights shortly after...
Regards
OV