After spraying the basement I decided to put an opening in the top of the staircase at the back, leading from the basement to the ground floor. I knew it wouldn't be easy but I also knew it would bug me forever more if I didn't do it.
The opening will be at the top of those stairs in the basement up to the ground floor of the house.
The first thing was to measure the top of the basement and the bottom of the house to ensure the two openings would match up with each other. I'm not very good at this sort of thing, I often get things the wrong way round, so I had to concentrate!
Once I was confident that my measurements were accurate I drilled holes round the edge of the opening
sawed in between the holes
pushed the drilled piece through, and sawed and filed the edges
then did the same with the basement.
My MO was slightly unorthodox, basically using anything that would do the job.