Need more information like where you found it, in what context (planecrash, battlefield, etc), and size.
Not sure, but here's a guess.
BSA was involved in turret manufacturing for tanks and howitzers. Not sure if they worked the airplane aspects, but perhaps so. It looks like the foot stirrup and pedals (left and right) for a gunners station. The stirrup is stippled with a rubber non-slip coating to keep the gunners feet from inadvertently sliding off. The pedals likely were used to translate the turret or gun mount. You can see that the pedals are slotted to accept cable rigging that likely connected to a solenoid initiating motor assist for the gun mount translation. While there is some wear on the foot stirrup, whatever this is the stirrup does not appear to have received years and years of use under the gunners boot.
The metal is in relatively good shape. Any more information?