Lewis,
The ONLY thing you should be aware of is that if you are within 50feet of the centre of a public highway (or back lane in your case) is that if someone walking past hears your gun being fired and it "Scares" them, then you are committing an offence. But you seem to have that angle covered by checking before you are firing
If you/your stepfather were to ask someone to wait until you've taken the shot you may think thats good, but in actual fact, you are hindering them and again if that person whinges to the police, then again an offense has been committed Its very very complicated