Air Ministry, at this time I won't discount any theory. I can tell you that the Siskin had 2 battery types: a No.0, Mk III of 2v (typo?); and a No. 3 Mk III of 12v. I have yet to find a description, or better still a dimensioned diagram, of either. That information would make it easier to 'guesstimate' where they were located.
Thank you for your thoughts.