Years ago there was a similar situation in Burgess Hill, they built a hoofing great Tesco but someone forgot to buy the bit of waste land that would have joined it to the easiest road to get to it other than going right around the town.
The guy that owned it sat still, played the waiting game...
There is actually a gate there already, I've used it when walking from The Swan back to the Amex.
No idea what it's for though, it just goes straight into the trees.