The origin of the trees planted all around the field:

Looking into the bit on trees on the field brought back the image of dozens of lads at break time heading across the field towards those trees between Ernie's hut and the pavilion and mysteriously disappearing. This was no Bermuda Triangle however simply the means whereby we could all enjoy a fag perched on top of the fence behind the trees with our bodies, and the smoke, hidden from view. Pete Jackson (1955)