I have read the open letter of complaint. My comments here relate only to the astronomical matters raised - I do not claim expertise outside my field (carbon dating etc.). At the time of writing, I have not yet seen the Horizon program, so cannot form any judgement concerning fairness.

I do not agree with the following arguments in the letter put forward by Graham Hancock and Robert Bauval.

First concerning the "bending" of Orion's Belt:
As my colleague, Ed Krupp, has pointed out, the Belt in the sky "bends" towards the South, whereas the ground layout of the pyramids "bends" towards the North.
I understand (and predicted) the explanation now put forward by Graham Hancock that it is because a picture seen up in the sky has been transferred (without reflection) to the ground. However, if Hancock and Bauval were to adopt such an explanation, they would shoot down their own claim (Keepers of Genesis, pp 71- 72), that it is a match of the pyramids AND THE NILE. Their diagrams in the book show the pattern to be MIRRORED - and NOT as in the explanation in the letter of complaint.

Next in regard to the angles of Orion's Belt:
I still maintain that the tilt of Orion in 10500 BC is some 10 degrees different to the layout on the ground, and therefore the term "precisely matched" is inappropriate.
I was shown, and commented on, copies of the emails that Robert Bauval sent to the BBC in July, but they give a different explanation to that included now with the letter of complaint. I would have liked to have seen Robert Bauval publish those previous explanations!
I have, in my letter to "Astronomy and Geophysics", made it clear as to how I measure the angles. If, as Robert Bauval now argues, one rather takes the two larger pyramids, then a rough match could only be achieved by discarding the one of the three pyramids (Menkaure) and one of the three stars (Alnitak), and working with only two pyramids and two stars, I find that even more unconvincing.

However, in general, I do support the association of the star shafts in the Great Pyramid of Khufu with star patterns, and Orion in particular. It is the claim regarding the 10500 BC date that I dispute on astronomical grounds. While I cannot say I approve of the manner in which this material has been conveyed to a public audience, I do recognise that it has brought about considerable interest in both pyramids and stars.