That's a great air rifle you have there. That looks in good shooting shape. Fortunately, they aren't very sought after by collectors, probably because in the 30's they were the budget alternative to the under levers, plus there was only one model of them.
However they are well made, fine shooting air rifles, that are easy to shoot and handle very nicely. A lady I used to go out with really liked shooting mine. I would rate them as good as any of the other prewar british break barrels.
Power wise they would be maybe seven or eight foot pounds in good condition. I have seen a couple with the front part of the cylinder where the jaws that hold the barrel, be slightly loose. As the the jaws thread onto the cylinder. But a drop of thread lock would sort that.
"helplessly they stare at his tracks......."