Hello to OP and other commentors. I came across the site and this post by chance having done a Google search for 'bushy hill', having seen it labelled by that name on Google Earth.
We always referred to it as Radar Hill locally (just as OP original review mentions). I thought I would provide an anecdote about this place that you might find interesting. Back in the early 2000's, prior to 2005. Let's say...I 'knew some people' who were active in the pirate radio community in Essex. As ill informed as aforementioned people were, they did appreciate that height equalled broadcasting distance. So in relatively flat Essex any kind of site that was a bit taller than average terrain was fair game.
The radio station in question had a brief spell broadcasting from one of the more contemporary towers for a stretch of a few weeks or a month or so. At that time they would access the site not by coming directly up the concrete track off of Edwin's Hall Road, but by crossing the fields directly to the North and slipping in through the tree line adjacent the masts. We had no idea whether the masts were 'active', or even what the base was being used for at the time. Only that it may have had some military or Government connection. In retrospect a pretty foolish place for an installation when considering who might have been running the site! 'They' must have been quite young and naive at the time.
Crossing the fields back then meant on one occasion disturbing an entire heard of cattle that were laid prone and who subsequently stood up and moved towards them whilst mooing. I'm told that a heard of dairy cows bearing down on you in the pitch black is fairly intimidating not to mention counter to what you might want during a stealth approach.
I can't remember exactly which mast was used, but that at the time I believe it had a small enclosed box at the top (maybe made from GRP or similar?) that was just big enough to squeeze inside of (although I notice from current pics these are no longer present - so hoping I'm not confusing this with somewhere else - they did get around a bit). This was very convenient for stashing a transmitter out of the elements and had the added bonus of having a 240v supply (they were used to running their own, new 240v up a mast from ground level somewhere). The other hugely convenient feature of the mast was that it had a winch at the top! Back then, they used to install the transmitter inside of a locked safe to prevent theft by other radio stations. So that made getting the very heavy safe up to the top much easier.
The site didn't pan out for them not because of the operators of the site getting wind of the 'extra installation' on the mast of their own accord, but because a competitor radio station stole/dismantled, or at least caused enough of an issue at the site whilst trying to track the transmitter that the radar base operators became aware of what was going on.
I had to wonder whether or not there was any link to the pirate radio operations and the alleged motion detection that the site now has when I read above about someone else's near run in with the police. Although it may not be linked of course.
They never had any issue whilst doing recces or installing. Remarkably. A really interesting place and I'm surprised at just how little seems to be known about what goes on there to this day. I would certainly not recommend repeating any of this - I think even very clean transmitters installed in poor proximity to other equipment can cause interference and so what they did was highly irresponsible and they wouldn't have done it if they could wind the clock back.