If you look at the Thames Valley Police Freedom of Information Response, Investigation into the death of Dr David Kelly - RFI2011000421, it seems clear that four people were on board.
I've quoted the question and answer below:
Investigation into the death of Dr David Kelly
29 June 2011, 3:49 pm
This request, reference RFI2011000421, was received on Tuesday 07 June 2011, 3:49pm.
Who was on the helicopter that landed at Harrowdown Hill on 18th July 2003?
The following personnel were on board:
1 x Pilot
2 x Observers
1 x Thames Valley Police employee on day attachment.
So far, so banal.
But it becomes more interesting if you compare that "four" with another Freedom of Information Response to a question I asked in October 2010.
I'm pasting part of the helicopter log here:
Notice the three pieces of black redaction, each of which refers to s40 i.e. Section 40 of the Freedom of Information Act.
Section 40 relates to personal information. In other words, the redacted material relates to three names.
The PDF file comes from here: Investigation into the death of Dr David Kelly - RFI2010000727. Scroll to the bottom of the page to click on the PDF file. The relevant information is at the top of page 5.
However, how does one explain the discrepancy between "three" and "four"?
My hypothesis is that someone got on the helicopter when it landed at Harrowdown Hill at 10.55 on 18th July 2003 or someone got off the helicopter when it landed at Harrowdown Hill at 10.55 on 18th July 2003.
It's almost enough to make you imagine that Thames Valley Police didn't want us to know about it.
Who got on the helicopter?
Who got off the helicopter?
Perhaps one day Thames Valley Police will be honest enough to tell us.