Interesting bit of information about Dennis Hayley-Bell, thanks! Does that also mean that I got his first name correct then?
As for observer Chris Mullen, I've had a quick look and have his name spelled this way in an article written by Sir George on the occasion of the VC10's 25th birthday (see here:
The VC10 - 25th Anniversary that page on my site is mostly a verbatim copy of the text that was included with a special philatelic cover). I could check some other sources but I remember seeing it written as 'Mullen' in several places. Perhaps a different Chris?
Edit: I've also just added Flight Test Engineer Dick Storey, his name was hiding in plain sight on my site here:
http://www.vc10.net/Photos/early_days.html