What is this weapon? Looks like a very hefty foundation.

This is a Blacker Bombard Spigot Mortar on a concrete mounting.
Blacker Bombard - Wikipedia
This link has the same photo labeled:
Home Guard soldiers operate a 'Blacker Bombard' spigot mortar during training at No. 3 GHQ Home Guard School at Onibury near Craven Arms in Shropshire, 20 May 1943.

 

http://ww2talk.com/index.php?search/7288960/&q=blacker+bombard+spigot+mortar&o=relevance

Hours of reading here Dave - find a nice restful spot and away you go

TD

 

In the 21st century used for art
In a back garden in Shropshire covering a river bridge
Photos in posts from my collection

 

In Amersham Buckinghamshire along side a foot path in the 21st century

 

Did you recognize it as a mount when you took the picture? Probably did.

Kind of a subtle 'Swords into plowshares' image.

 

Sadly Dave I did
been trawling around bits of the UK for all WW2 related buildings and other bits
Many many posted here United Kingdom


Regards
Clive

 

I hate to be a pushy sod, but this might be of interest to you:
Maybe of interest: Spigot books and talks!