I agree with rekstout. Unless there's a contract in place or another document that can prove he gave you the idea he has no claim. I actually had the same idea a few years back but there was much confusion with a few other bodies and some marketing... do I now claim IPR from you? No, and that's because there's no proof that I thought of the idea before you, gave you the idea and you stole it, or that you caused me financial loss by that theft. His claims are useless in court unless backed by irefutable proof, and if he's worth his salt he'll be trying to register his IPR with a solicitor ahead of you - in which can go to a solictor's office and get them to time stamp and store a document for you that proves your ownership of the concept before he can. However, above all this, I should tell you that this isn't a unique product and it already exists in many organisations - it's not actually a concept that either of you have ever owned so tell him where to go :-) He also sounds just like a person I contract for... I'd LOVE to know if it's the same person!!!