Nice looking old frame! Honestly, I am not sure on the make. Maybe a shot from the top of the seat stays where the wheel fits in might help. Then again, someone else might be able to ID it on what you've posted.
It's similar to late 30s frames by Shelby, Cleveland Welding, Colson, and Schwinn. But, it doesn't quite seem to be any of them. My guess would be Manton & Smith, but hopefully Phil/rms37 will see it and set us all straight! -Adam