In message , TheScullster
writes

The beam is to be installed perpendicular to the walls at each end and
supported on the "inner leaf". This is to allow removal of a single block
wall (which spans the width of the room) used to support ceiling joist
joints.
As this forms remodelling of an existing extension, this means that one end
sits on the original house outside brick wall and the other on the internal
extension block wall.

Umm.. nothing to do with pad stones but, you did mention a conventional
roof. Is there any chance that the ceiling joists are tieing the feet of
the rafters? Or have I misunderstood the scheme:-)

regards

--
Tim Lamb