The LNER Encyclopedia

During a recent walk along part of the old Grantham to Lincoln line I came across this object in the undergrowth.
I'm not sure if it is of 'railway origin' but if anyone can identify what it was I would be most grateful.

It's dimensions are approx 8" (200mm) square base. Top to bottom about 10" (250mm)

Thanks in anticipation.

Is it the non plug end of an ETH cable?

It’s not railway related. It’s an air release valve that would be located on a water main at a high point. Inside is a wooden or rubber ball that when the water main is empty drops down allowing air to escape as the main is filled with water. The ball rises up on the water and seals an opening at the top.