Looking at an enlarged scan of the photos, I still can't make out the function of the mound in front of the control tower. It could be a bomb-shelter, but the brick structure doesn't look right, unless the earth mound under which these things were normally buried has become worn away. It looks as though long grass has been allowed to grow on the top of the edifice. In between the mound and the edge of the airfield is a set of markings like a giant smiley which I assume was the Station identification. In front of the mound a row of folding chairs is laid out with the ends turned in, but no-one is sitting on them.
Have a look for yourself. Someone must know the answer:
I also remember looking at the ORB for Benson for V-E Day 1945 a few years back. Apparently during the celebrations that night a substantial proportion of the camp's transport was hijacked and raced around the airfield. Whether any damage was done I can't remember. For V-J Day a few months later someone had the presence of mind to immediately order that anything and everything possessing wheels should be rounded up. The whole lot was corralled under guard in the centre of the airfield to prevent mischief.