This is a website that is not only excellent in its own right but some of its photographs illustrate Harrowdown Hill and the surrounding area http://www.geograph.org.uk/
As you can see it's a project to collect geographically representative photographs and information for every square kilometre of Great Britain and Ireland.
(I'm aware of readers of this blog from many countries other than the UK. It's possible that maps of your own nations work on different principles to those used by the Ordnance Survey in this country. Here the maps contain light blue horizontal and vertical lines which are one kilometre apart. Hence the logic of taking photographs in each of these identifiable squares and being able to reference the locations of the resulting images)
Rather than actually displaying the images here I'll provide the relevant links. One of the useful features is that the date of each photograph is given thus allowing some sort of assessment of the amount of vegetation that would be present in July - a time of near maximum growth.
Luckily there are a number of images that give us a good idea of the appearance of the route taken by the volunteer searchers once they had left their car.
This is part way along the unmade track to Harrowdown Hill that the searchers would have walked up with Brock. The photo was taken in August 2009 with the ground looking fairly hard, I would imagine in winter it could be quite muddy.
Taken a couple of months after Dr Kelly's death it shows the track still well defined but with somewhat different vegetation either side
Dr Kelly's body was found well into the northern part of the wood on Harrowdown Hill and these next two images appear to be further south although within the wood. I am placing them here because I think that they may be within that part of the wood looked at by the searchers before they went on down to the River Thames.
The searchers would have arrived at the river by the path that enters the photograph centre right. Much of that riverbank vegetation is Himalayan Balsam I think and would be at its maximum at the time that the picture was taken. Even in mid July it would be reasonably dense I would have thought.
This close up of the signpost was taken in May
Another August shot, this time of two different sorts of craft on the river.
The "boat people" were moored close to this spot.
The wood on Harrowdown Hill is on the skyline. The right of way between the Hill and the Thames is a field path rather than the enclosed lane that was seen in the first two images.
There are more images of the area on the Geograph site if anyone wishes to explore further. hopefully though the links I've given will give a much clearer idea of the locality.