I do enjoy a good blue plaque - they can teach you a lot about a local area, and quite often you learn something new.
Joseph Flesher was the railway contractor responsible for the building of this stretch of the London to Brighton Line, and the Folly Hill Tunnel, which you're almost stood on. This spot was chosen because this was the former location of his house and garden before Haywards Heath existed - he was the first resident of the town.
The coordinates take you to the plaque, but since the image is available online, that would make things too easy! You are looking for some nearby information, where:
A = The number of tiers to the planter, minus 3
BC = the two digit number on the telecoms box, also to the left of the plaque
Now, those two are on Google maps. So...
D = look for a sticker with a phone number on the tall black planter. D is the sixth digit minus the seventh digit
E = the first number (there are four numbers on each cover, you need the first digit) on any of the three services covers next to the pedestrian crossing.
F = the last number on any of the three service covers.
And then, the coordinates are as follows: N51 (ExF).(C-D-A)(B-A-A)(CxF) W00 0(D+A).(C-B)(A+F)(E-B)
Limited parking is available on the roadside for a short period of time, slightly further along the road. At the time of publish, some inept driver had crashed into the rails on the road side of the footpath. The cache is still in place however, and the hint still applies. Phew!