Simon, I'd like to think I am a desent and honest human being who is kind to animals, but with the phrase "National Contractor who is doing you out of work" I have no dilemma, moral or otherwise. he gets your work you get his gear, sounds like justice to me!
A local window cleaner? Then I would go to great lengths to return it, perhaps asking at the petrol station first if they have his name and phone no. (Not telling them why or one of them will have it and blame you)
PS. If Wylie doesn't offer you a fair price give me a shout!