Need a few more answers, Ron. First, I guess this is 2-storey, and we're talking about a downstairs room. In the dim past, it was quite normal to have no lintels over upstairs windows. The roof framing spanned easily.
Assuming 2-storey, if you have a solid wall (no cavity), then an external flat, brick arch could be supporting the inner part of the wall. Not ideal, but not quite so onerous.
!930s, I would assume it is cavity though. I see what Jack was after. A brick "soldier" arch externally (bricks standing up on end) would support the external leaf.......... but not the internal. That's why the lintel is needed.
Back in the 30s, large picture windows or bay windows were constructed to be partly structural. That is, the timber sections were such that the frame could support a load. I'm guessing that the DG Company took the window out and replaced with modern uPVC.
Modern uPVC windows are not usually structural. This is where the problem arises.
Inserting a lintel above the window is no big problem....... providing there is enough distance between the top of the window and the ceiling.