Any Ideas? Near Spittlegate

I have a feeling this has been covered somewhere, but in any event any ideas as to what this is, it is just at the back of the Kesteven Rugby Club.

there is a small surface building and what looks like a steel underground tank, what is rather odd is the concrete block that has been dropped on the tank, it seems to be rather new concrete.

The site appears to be marked on the 1921 OS 1 inch sheet

I am sure there is a simple explanation

Behind the clubhouse? Outside the playing fields; north, south?

I see a couple of small structures but looking on oldish maps (not OS) I can't see anything marked.

www.flashearth.com/?lat=52.893199&lon=-0...&z=17.7&r=5&src="msl"

behind the Rugby Club, access via the lane up from Little Ponton

Definately marked on the 1921-1922 OS sheet (well the Cassini repro), I do think I am repeating myself!